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[This list as pdf-file]
Abstracts
Key:
1.1 after the abstract indicates Talk 1 in
Session 1
PSA-1 indicates Poster 1 in Poster Session A
PSB-1 indicates Poster 1 Poster Session B
The Detection of the Motion of Radio Meteor
Reflection Point of Geminids by HRO
Kouji Ohnishi (Nagano National College of
Technology,Japan), Toshiyuki Ishikawa, Shinobu
Hattori, Osamu Nishimura, Akiko Miyazawa, Masatoshi
Yanagisawa, Makoto Endo, Masaki Kawamura, Toshiyuki
Maruyama, Kai Hosayama, Mai Tokunaga, Yoshie Aoki,
Yukiko Iijima, Aya Kobayashi (Nagano National
College of Technology, Japan), Kimio Maegawa (Fukui
National College of Technology) and Shinsuke Abe
(Institute of Space and Astronautical Science,
Japan)
Ham-band Radio Observation (HRO) is one of the
observational techniques of the forward scatter
observation of meteors. We observe the meteor echo
with two-element loop antennas (F/B ratio is 10 dB)
at the Nagano National College of Technology
(Nagano, JAPAN) using the continuous transmission
of beacon signals for meteor observations at
53.750MHz, 50W from Fukui National College of
Technology (Sabae, Fukui, JAPAN). To prove that the
radio echo is really the echo due to meteor, we
construct the Directional Determination System
using the paired antennas that can detect the
direction roughly where the radio echo come from.
The direction of one of this paired antennas was
West toward Sabae and the other was East which has
proved to be the most sensitive for this research.
Using this system, we detected the change of the
direction of reflection point of meteor radio
signal of Geminids in 2000; from the westward to
eastward before and after the culmination of the
radiant which is consistent the formula of
reflection point of meteors. At the same time, we
detected the change of a trend of the Doppler shift
of meteor echos. This result is consistent of the
meteor wind data of MU Rader of Radio Science
Center for Space & Atmosphere (RASC), Kyoto
University. PSB-5
The Earth Rotation and Revolution Effect of the
Daily and Annual Variation of Sporadic Meteor Echo
by HRO
Kouji Ohnishi (Nagano National College of
Technology ,Japan), Shinobu Hattori, Osamu
Nishimura, Toshiyuki Ishikawa, Akiko Miyazawa,
Masatoshi Yanagisawa, Makoto Endo, Masaki Kawamura,
Toshiyuki Maruyama, Kai Hosayama, Mai Tokunaga,
Yoshie Aoki, Yukiko Iijima, Aya Kobayashi (Nagano
National College of Technology, Japan), Kimio
Maegawa (Fukui National College of Technology,
Japan) and Shinsuke Abe (Institute of Space and
Astronautical Science, Japan)
Ham-band Radio Observation (HRO) is one of the
observational techniques of the forward scatter
observation of meteors. We started the observation
of the daily and annual variation of sporadic
meteor echo with paired two-element loop antennas
(F/B ratio is 10 dB) at the Nagano National College
of Technology (Nagano, JAPAN) using the beacon
signals at 53.750MHz, 50W from Fukui National
College of Technology (Sabae, Fukui, JAPAN) from
Aug.2000. The direction of one of this paired
antenna was West toward Sabae and the other was
East. This system could be roughly detected the
direction of the radio echos. Using this system, we
observe the daily variation of sporadic meteor
echos; the echo rose from midnight with the peak
coming at about 6 a.m. and decreasing to the noon,
the peak echos were observed from the West antennas
at 4 a.m. and the peak from East antenna was at 10
a.m. This daily variation is interpreted as the
effect of the Earth rotation and revolution around
the sun. At the conference, we will also discuss
the annual variation of sporadic meteor echos.
PSB-6
Fine Structures within the Leonid Dust Trail:
Resonant Filament Model Examined by Optical Video
Observations
Hajime Yano (Institute of Space and
Astronautical Science, Japan), Shinsuke Abe
(Institute of Space and Astronautical Science,
Japan) Noboru Ebizuka (The Institute of Physical
and Chemical Research, Japan) Norimoto Fujino
(Science University of Tokyo, Japan) and Jun-ichi
Watanabe (National Astronomical Observatory,
Japan)
We observed the Leonid meteor showers by
real-time video imagery of high definition digital
video cameras with image intensifiers (HDTV-II)
onboard airborne platforms (Leonid MAC) in 1998
(over the Pacific)-1999 (over the Mediterranean),
and NTSC digital video CCD cameras (WATEC) placed
at a 2500-m class mountain in the Canary Islands in
2000. HDTV-II and NTSC videos had different
limiting magnitudes for meteor detection (e.g., the
8th mag. for HDTV-II with a f1.0 50-mm lens) but
both indicated fine structures (in several to a few
tens of minutes) of the flux variation within each
main peak. Such trends became more evident as the
magnitudes of observed Leonids went fainter.
Recently Cevolani and Pupilo reported radio
observations of the 1999 Leonids from Italian
ground stations also found the same as our results.
These temporal flux variations seemed to coincide
with periods that the Earth crossed the
"inhomogeneous" Leonid dust trail, which is
composed of the smoothed "background" component and
several narrow, "dust filaments" ejected from the
parent comet P/Tempel-Tuttle in the last several
perihelion passages. Thus, our results directly
confirm the resonant cometary dust trail model
proposed by McNaught and Asher in 1999, especially
in the smaller end of the Leonids. PSA-24
[To top of page]
Spectroscopic Study of Meteor and Persistent
Train
Shinsuke Avell Abe (1), Jun-ich Watanabe (2),
Hajime Yano (1) and Noboru Ebizuka (3)
1) The Institute of Space and Astronautical
Science; 2) National Astronomical Observatory; 3)
The Institute of Physical and Chemical Research
During the 1999 Leonid, an intensified HDTV
camera was used for slitless meteor spectroscopy at
visible and near-UV wavelengths in the Leonid
Multi-instrument Aircraft Campaign. The HDTV system
provided a high dynamic range (digital 10-bit) and
a wide field of view of 37 x 21 degrees. Here, we
report on the results for several particularly nice
spectrum from Leonid and Taurid meteors. Fe/Mg
abundance of Taurids is about 2 times higher than
that of Leonids. It is possible to build up a
hypotheses. A LTE temperature calculated by
numerous Fe emission lines below 550 nm is compared
with a electronic-vibrational temperature of N2 in
the visible (550 &emdash; 800 nm). It seems that
meteor spectra can be explained well by LTE model.
Moreover, stereoscopic observations of one
spectroscopic meteor have been accomplished during
the Leonid MAC and the real height of emissions
were measured. An excellent spectra of a Leonid
persistent train was obtained during the 1998
Leonid maximum in Japan by using a grating
spectrograph covering 370 &emdash; 640 nm
wavelength range. Identified Mg, Fe and Na suggests
that these atoms are the source of the persistent
trains and of long-lived emitters. 4.1
Orbital Perturbations on Dust Trails: Predicting
Meteor Storms
David Asher (Armagh Observatory, UK, and Bisei
Spaceguard Center, Japan)
Although the chaotic nature of planet-crossing
orbits limits the timescale over which their
dynamical evolution can be reliably calculated, a
sufficiently accurate initial orbit can at least be
followed for some time (e.g., centuries) into the
future. When debris is released from a comet during
a given return to perihelion, the first stage of
its evolution is to stretch gradually into a long,
dense, narrow trail of meteoroids and dust.
Perturbations on particles in the trail are a
function of position along the trail, and position
along the trail depends almost entirely on orbital
period, particles of shorter/longer period being
ahead/behind. Therefore perturbations at all points
along the trail, and their consequent effect on the
trail's location, can be reliably calculated until
chaotic behaviour sets in (e.g., for some
centuries). Since meteor storms occur when the
Earth passes near the centre of a trail, where the
particle density is very high, this has allowed
storms and outbursts to be predicted with great
accuracy in the Leonids and many other streams.
2.1
Features of the Enhanced AMOR: The Advanced
Meteor Orbit Radar
W.J. Baggaley (Department of Physics and
Astronomy, University of Canterbury, Christchurch,
New Zealand)
AMOR is a continuously operating radar facility
for measuring the heliocentric orbits and
atmospheric parameters of Earth-impacting grains
down to sizes of 40 micrometres. The facilty
provides a data base of the order of 10^6 orbits.
Recent extensions to the facility including
augmented antenna arrays and increased velocity
resolution are providing an enhanced system
capability. 6.1
Mapping the Interstellar Dust Flow into the
Solar System Using AMOR
Jack Baggaley (Department of Physics and
Astronomy, University of Canterbury, Christchurch,
New Zealand)
The Advanced Meteor Orbit Radar facility (AMOR)
monitors the dynamical properties of meteoroids of
sizes down to about 40 micrometres. The orbital
data set secured to date contains about 10^6
orbits. The population of inner solar system
meteoroids sampled contains a significant
proportion of particles that are moving in unbound
solar orbits. Maps the far-sun inflow directions of
this extra-solar system population show the
presence of both a broad interstellar inflow and
discrete sources. 11.6
Combined Visual and Radar Observations. 45 Years
Later
O.I. Belkovich (Zelenodolsk Branch of the Kazan
State University, Russia) and V.S. Tokhtas'jev
(Engelhardt Astronomical Observatory, Russia)
Combined visual and radar observations of
Perseids made by B.A. Lindblad at the Onsala Wave
Propagation Observatory, Sweden between 1953 and
1961 have been processed taking into account random
positions of reflecting points on meteor trails and
the modern physical theory. As a result the new
more accurate relation of ionization and luminosity
coefficients has been found for Perseids meteors.
Velocity dependence of this relation was found from
the analysis of other data. PSA-4
Comparative Analysis of Meteor Shower
Observations Processed by Three Different
Methods
O.I. Belkovich (1), M.G. Ishmukhametova (2),
N.I. Suleimanov (3) and V.S. Tokhtas'jev (3).
(1) Zelenodolsk Branch of the Kazan State
University, Russia, (2) Kazan State University,
Russia, (3) Engelhardt Astronomical Observatory,
Russia
Long-term series of radar and visual
observations of Geminids and Quadrantids have been
used for the analyses. Processing of radar
observations has been made by the two methods: 1)
the flux density has been calculated from hourly
number of meteors with amplitudes exceeding the
radar threshold level, 2) from hourly number of
reflections from overdense meteor trails with
durations greater than 1 second. The S coefficient
of meteoroid mass distribution as a function of the
solar longitude has been found from rations of two
flux densities. Reduced zenith hourly rates for
meteors brighter than +3 magnitude from visual
observations of the showers have been found by the
method worked out at the Engelhardt Observatory.
Profiles of the showers (flux densities or ZHR as
functions of the solar longitudes) depends on the
minimal registered masses of meteoroids. This fact
has given us the opportunity to check as the
correctness of the methods of processing of
observations so to do independent estimation some
parameters of the physical theory of meteors (mass
scales of radio and visual meteors). The estimation
of the collecting area in visual observations of
meteors has been made also. PSA-5
Expected Distribution of Interstellar Meteoroids
in the Vicinity of the Earth's Orbit
O.I. Belkovich and A.R. Bagautdinova
(Zelenodolsk Branch of the Kazan State University,
Russia)
One of the hypotheses of origination of
interstellar meteoroids is the lost them by
planetary systems of the late spectral class stars.
In this case the most probable distribution of
their velocities relative the local centroid of
stars mast be similar to one of the late class
stars. This distribution has been found from the
catalogue of star ray velocities. The orbital
element distributions of interstellar meteoroids in
the vicinity of the Earth's orbit and radiant and
velocity distributions over the celestial sphere in
the heliocentric and geocentric frame of references
have been calculated taking into account of
meteoroid flux transformation due to the Sun
gravitation field and moving the Sun and Earth
relatively the local centroid of stars. PSB-22
[To top of page]
Is the Problem of Sporadic Meteoroids Space
Distribution Solving Correct?
O.I. Belkovich (Zelenodolsk Branch of the Kazan
State University, Russia)
Nearly all that we know now on the distribution
in the interplanetary space of sporadic meteoroids
in the mass range from 0.00001 to 100000 g is based
mainly on the ground-based meteor observations. We
used to think that this problem was solved years
ago except for some details. I would say that it is
a delusion and I would like to prove that
assertion. Firstly. What variable or what variables
can represent the distribution of sporadic
meteoroids in the vicinity of some point of the
space? As a physicist I can say that it is the
phase density, i.e. density of particles in the
6-dimensional space of coordinates and velocities
as a function of their masses. What corresponds now
in the meteor astronomy to this definition?
Secondly. All ground-based meteor observations are
made on the moving and attracting Earth. Are you
sure that so-called astronomical selection taken
into account in processing of observed data is
correct? Thirdly. Most meteor astronomers like to
analyse their own observations and even in case of
some differences with the results of other
observations they are inclined to explanation of
those differences due to the different observed
masses of meteoroids. Do you believe them? 10.2
The Moravka Meteorite Fall: Fireball Trajectory,
Orbit and Fragmentation
J. Borovicka, P. Spurny and Z. Ceplecha
(Astronomical Institute, Academy of Sciences, 251
65 Ondrejov, Czech Republic)
The Moravka meteorite fall of May 6, 2000, is
only the sixth case in history, when the pre-fall
trajectory could be determined from instrumental
records. A very bright fireball appeared during
broad daylight at 11:51:52 UT and was seen by
thousands of people. Fortunately, three casual
witnesses captured the fireball on video. The
fireball was also detected by satellite-based
infrared and visible sensors. Sonic booms were
recorded by a local seismic network and an
infrasound array located in Germany recorded
signals from this event. Three ordinary chondrites
of type H5-6 and total mass of 634 g were recovered
in the vicinity of village Moravka, Czech Republic
(18.53E, 49.60N) over a span of 11 km. Much more
fragments certainly fell, since one video record
shows multiple hierarchical fragmentation to more
than hundred pieces. After a careful calibration of
the videos, we were able to determine the fireball
trajectory with a good precision. The initial
velocity was 22.5 km/s and the trajectory slope 20
degrees to horizontal. The most resistant fragment
disappeared at an altitude of 21 km when
decelerated to 4 km/s. The heliocentric orbit is
notable by a high inclination of 32 degrees.
Details of fireball dynamics and fragmentation will
also be given. 8.1
Video Spectra of Leonids and Other Meteors
Jiri Borovicka (Astronomical Institute, Academy
of Sciences, 251 65 Ondrejov, Czech Republic)
More than thousand Leonid video spectra were
obtained during the expeditions in the years
1998-2000. A survey of the spectra with the
emphasis to the effect of early release of sodium
will be presented. Leonid spectra will be compared
to the spectra of other meteor showers obtained
with the same instrument at the Ondrejov
Observatory. PSA-20
ALIS (Auroral Large Imaging System) Used for
Optical Observations of the Meteor Impact
Process
Urban Brändström (1), Björn
Gustavsson (2), Åke Steen (3) and Asta
Pellinen-Wannberg (1)
1) Swedish Institute of Space Physics, Kiruna,
Sweden; 2) National Institute of Polar Research,
Tokyo, Japan; 3) RemSpace Group, Linköping,
Sweden
ALIS is a low-light imaging facility consisting
of six remote-controlled stations in northern
Sweden. The initial objective of the facility was
to study aurora from multiple directions and
reconstruct three dimensional distributions of the
phenomena with the tomographic inversion method.
The stations are located in a 50 km grid. They are
equipped with non-intensified, high-performance CCD
cameras, with telecentric lens systems and
filter-wheels with narrow-band (40 Å)
interference filters for auroral emission lines.
The field-of-view is 90° x 90° at two
stations and 54° x 54°at four stations.
Each camera is mounted in a positioning system,
enabling ALIS to monitor overlapping
fields-of-view. The facility can also be used for
real time meteor impact observations. Filters for
optically observable meteor constituents such as
sodium (5893 Å) and calcium (4227 Å)
can be used at two stations, while the others
measure the trail impact in white light. When a
meteor comes within the common volume its ablation
can be observed by making multiple exposures before
reading out an image. Exposure times down to 50 ms
and frame rates of one image per second are
possible. A simulation of how an ablation process
of sodium and calcium can be observed with this
facility is presented. PSA-30
Meteor observations from Israel
Noah Brosch (Wise Observatory, Tel Aviv
University, Tel Aviv 69978, Israel)
We observed meteors of the Leonid and other
showers with an L-band radar system. In the case of
the 1999 Leonids we detected a twin-peaked dheight
distribution, where the surprising finding was of a
wide peak centered near 250-km altitude. We present
a possible mechanism to generate radar returns at
such heights. We also describe the development
status of a two-station system to observe video
meteors, which is planned to operate in the second
half of 2001. 2.7
Astronomical and Physical data for
Micrometeoroids Recorded by the ALTAIR Radar
P. Brown (Los Alamos National Laboratory, Los
Alamos, New Mexico USA, and Department of Physics
and Astronomy, University of Western Ontario,
London, Ontario, CANADA), S. Hunt and S. Close (MIT
Lincoln Labs)
We present preliminary results of orbital and
physical measurements of a selection of meteoroids
observed at multiple frequencies by the ALTAIR
radar on Kwajalein island in November, 1998. The
head echoes observed by ALTAIR allow precise
determination of velocities and decelerations, from
which both ballistic parameters for individual head
echoes and orbits have been measured and will be
presented. The ALTAIR radar observes several
thousand head-echoes per hour and each head echo
has a known trail orientation relative to the beam.
Examination of the trail orientations produces an
estimate of the effective beam collecting area.
This collecting area when taken in conjunction with
the observed rate information, allows an
independent estimate of the limiting observed mass
of meteoroids observed by ALTAIR through comparison
with the known sporadic meteoroid flux. The
principle function of ALTAIR is as a contributing
sensor to the US Space Command satellite-tracking
network. ALTAIR is a high-power (5 Mw peak at both
frequencies), narrow beam (3° at VHF,
1.2° UHF), 43-m diameter mechanically steered
dish. ALTAIR transmits right circular polarized
energy and records left circular with a range
resolution of 15 m VHF and 7.5 m UHF meters.
Azimuth and elevation difference channel data are
also measured, which contribute to the accurate
determination of target position in three
dimensions. The aforementioned characteristics
allow ALTAIR to reliably detect a -62 dBsm target
in VHF and a 81 dBsm target at UHF at a range of
100 km. Examples of the head echoes observed by
ALTAIR and some indications of the likely origin
for the population observed by ALTAIR during this
campaign will also be discussed. PSB-9
[To top of page]
Recent Infrasonic Observations of Large
Bolides
Peter Brown (Los Alamos National Laboratory, Los
Alamos, New Mexico, USA, and Department of Physics
and Astronomy University of Western Ontario London,
Ontario, Canada), Douglas O. ReVelle and Rod
Whittaker (Los Alamos National Laboratory, Los
Alamos, New Mexico, USA)
We expect a minimum of several dozen bolides to
impact the Earth each year and penetrate low enough
in the atmosphere to produce infrasonic waves.
These objects have energies from 10-2 kT to many
hundreds of kT and many of these are also
simultaneously observed by US DoD satellites. Here
we present a summary and discussion of more than 15
infrasonically observed bolide events detected
since 1996. These data demonstrate the capability
of infrasound arrays to reliably locate the source
of bolide explosions in the atmosphere at heights
of typically 20-30 km and at ranges exceeding
5000km. We find, for example, that a 0.2kT bolide
detonation can be detected at ranges of 3300 km
under good conditions. Most notable among these
recent events is a multi-kt event recorded off the
coast of Mexico on 25 Aug, 2000 which was recorded
by six infrasound stations and a large (~20 kt)
detonation in the South Pacific on 18 Feb, 2000.
The modelling and interpretation of some individual
events and comparison with other instrumental
records of the same bolides will be highlighted.
PSB-14
The Tagish Lake Meteorite Fall : Interpretation
of Physical and Orbital Data
Peter Brown (Los Alamos National Laboratory, Los
Alamos, New Mexico, USA, and Department of Physics
and Astronomy, University of Western Ontario,
London, Ontario, Canada), Douglas O. ReVelle (Los
Alamos National Laboratory, Los Alamos, New Mexico,
USA) and Alan Hildebrand (Department of Geology and
Geophysics, University of Calgary)
The Tagish lake meteorite fell 18 Jan, 2000, at
16:43 UT in Northern British Columbia Canada. Some
500 meteorites were later found on the frozen
ice-surface of Tagish Lake. The fireball
accompanying the meteorite fall was widely recorded
by ground-based photographers/videographers,
earth-orbiting satellites, seismic and infrasound
sensors. The associated meteorites have proven
unique; reflectance spectra from Tagish Lake is the
first to match that of D-class asteroids (Hiroi et
al., 2001) and the bulk density of TL is the lowest
measured for any meteorite at 1.67 g cm-3
(Zolensky, pers comm). Here we will discuss the
data relating to the fireball and associated
modelling to determine the orbit of TL and probable
physical structure. Most notably, the fireball data
suggest that TL is intermediate between Type II and
III fireballs. Our modelling indicates the initial
body had a porosity near 50%. Type III objects are
presumed to be related to cometary bodies and
suggests that TL and by extension D-asteroids might
be intermediate in physical structure between
primitive chondritic asteroids and cometary nuclei.
8.6
Fragmentation and Initial Radius
M. Campbell and J. Jones (University of Western
Ontario, London, ON, N6A 3K7 Canada)
The problem of initial radius effects is one of
the major obstacles to well-calibrated fluxes from
meteor radars. The effects are dependent on the
wavelength of the radar used, and will be affected
by the dependence of initial radius on height and
the density profile of electrons in the ionized
trail. Most previous studies have assumed a
gaussian profile of electrons in the trail, and
have found from multifrequency studies that the
initial radius varies more slowly than the mean
free path with height. Studies of meteors in the
size range detected by most radars show that they
are not single bodies, but fragment prior to
luminous ablation; fragmentation is potentially a
huge effect in the initial radius correction. We
present a study of the effects of fragmentation on
initial radius using a combination of numerical
simulation and data from a multifrequency radar.
3.6
Ground-based Observations of the Leonids
1999-2000
M.D. Campbell, C. Theijsmeijer, J. Jones
(University of Western Ontario, London, ON, N6A 3K7
Canada), R.L. Hawkes (Mount Allison University,
Sackville, NB, E4L 1E6 Canada) and P. Brown (Los
Alamos National Laboratories Los Alamos, NM 87545
USA)
We present video observations of the 1999 Leonid
shower made from Israel and similar observations
collected in Spain and New Mexico for the 2000
shower. During the 1999 Leonid storm a total of 233
double-station Leonids were recorded. The mean
begin, maximum brightness and end heights are 123.3
± 0.7 km, 107.3 ± 0.42 km and 95.0 ±
0.56 km respectively for storm Leonids of average
mass ~10-6 &emdash; 10-7 kg. The peak flux at the
time of the 1999 storm was found to be 0.81 ±
0.06 meteoroids km-2 hour-1 brighter than +6.5.
using 15 minute binning and 0.99 ± 0.11
meteoroids km-2 hour-1 brighter than +6.5 for 3
minute intervals. The smaller temporal resolution
reveals a broad plateau in flux lasting from
approximately solar longitude=235.276°
&emdash; 235.285° (J2000.0). The video mass
distribution index over the course of the Leonid
storm was found to be constant constant near s=1.75
and near s=1.7 in 2000. The peak time of the storm
estimated from 3 minute resolution video counts
place the maximum at 235.281°±0.003°
(1h55m ± 4m). We do not find evidence for any
significant high altitude Leonid population in 1999
at video masses despite biasing one camera pair to
an intersection altitude of 160 km. The 2000 shower
showed two distinct peaks separated by 24 hours. We
recorded a peak video flux of 0.06 meteoroids km-2
hour-1 brighter than +6.5 near solar
longitude=236.15° during the 2000 Leonids. We
also discuss preliminary radar observations in 2000
which suggests that an earlier peak near solar
longitude=235.29 ± 0.02 is much stronger than
reported by visual observations and dominates the
later visual peak at 236.25 ± 0.02. PSA-19
Bolide Fragmentation Processes: Comparisons of
Bolide Data against Theoretical Bolide Models
Zdenek Ceplecha (Astronomical Institute, Czech
Academy of Sciences, Ondrejov Observatory,
Ondrejov, The Czech Republic) and Douglas O.
ReVelle (Los Alamos National Laboratory, Los
Alamos, NM 87545, USA)
This work is a practical extension and testing
of theoretical work also submitted to the
Meteoroids2001 conference. We have applied the
fragmentation model of ReVelle to the most precise
EN and PN fireballs in order to evaluate the shape
change parameter, and the fragmentation scale
height in comparison to the pressure or density
scale heights. If the ratio of the fragmentation
scale height to the density scale height is large,
we recover the single-body model limit. In the
opposite extreme, pancake type fragmentation is
possible. This was done in order to determine if,
for any of the available very precise bolide
observations, a parameter range existed that
allowed pancake type catastrophic fragmentation
processes to occur. This is important since a
number of workers in the early 1990's identified
this behavior as being important for the larger
bodies entering the atmosphere in the small
ablation limit (Hills and Goda, Chyba, Zahnle and
Thomas, etc.). We are currently examining a number
of bolides with very precise observations to
determine these fundamental properties and will
report on our findings at the conference. 8.4
[To top of page]
Bolide Fragmentation Theory with Application to
PN and EN fireballs
D.O. ReVelle (1) and Z. Ceplecha (2)
1) Los Alamos National Laboratory, P.O. Box
1663, MS J577, Earth and Environmental Sciences
Division, EES-8, Atmospheric and Climate Sciences
Group, Los Alamos, NM 87545, USA; 2) Emeritus:
Academy of Sciences, Astronomical Institute,
Observatory, 25165 Ondrejov, Czech Republic
The simple physical concept of the conservation
of energy and momentum (single-body theory) was
applied to a majority of multi-station photographic
observations of bolides assuming that the entry
behavior could be successfully described using a
constant value of the ablation coefficient (sigma),
the shape-density coefficient (K), and allowing for
a single sudden gross-fragmentation at one distinct
altitude. If the precision of the observational
data is better than +/-30 m in distance measured
along the bolide trajectory, then about 40% of the
events can be explained without any
gross-fragmentation, about 40% are explainable with
one gross-fragmention point and about 20% have
definitely experienced more than one
gross-fragmentation point. High values of the
derived ablation coefficients from observations
speak for nearly continuous fragmentation as being
the main mass-loss process for these bodies. If the
precision of the observational data is better than
+/-15 m as described above, then the assumption of
constant sigma and K is no more sustainable. There
are not many data available with such a high
precision. The complete solution of the problem
with sigma and K being functions of time was
subsequently derived and applied to 22 PN and EN
fireballs each with the needed high precision. The
luminous efficiencies, tau, can also be determined
from this approach as well. We will present our
results on sigma, K, and tau as a function of the
many different variables and parameters of the
problem for individual bolides during their
luminous trajectory and for individual bolide
types. PSB-11
Relation of Meteoroid Ablation-Classification to
Light Curves
D.O. ReVelle (1) and Z. Ceplecha (2)
1) Los Alamos National Laboratory, P.O. Box
1663, MS J577, Earth and Environmental Sciences
Division, EES-8, Atmospheric and Climate Sciences
Group, Los Alamos, NM 87545, USA; 2) Emeritus:
Academy of Sciences, Astronomical Institute,
Observatory, 25165 Ondrejov, Czech Republic
Classification of bolides according to their
ablation coefficients allows the recognition of 4
different groups: type I, type II, type IIIA, and
type IIIB. (In addition, iron bolides have also
been identified by the authors, but from our
limited data set, we can not evaluate them using
the current effort). The possibility of determining
to what type a bolide belongs from just light curve
data was examined, and a criterion IT =
(1/I)(dI/dt) was earlier proposed. The statistical
significance of sorting bolides according to IT was
also established. Recently, we have revised our
original light-curve classification using
ground-based radiometer data taken at the Ondrejov
Observatory provided by Sandia National Laboratory
(courtesy of Mr. Richard Spalding, operated by Mr.
Pavel Spurny) and have determined: a) the
originally proposed classification tables published
in the Annals of the New York Academy of Sciences
(1997) are valid and form the best possibility
available at the moment, but they should be
utilized only if light curves are the only form of
observational data available, b) relevant results
can be obtained for values of brightness separated
by a time interval, dt, of 0.05 s (if a shorter
interval is available, one should adjust the
interval by summing all data inside each 0.05-s
interval), c) associating a bolide with a single
type by using only light-curve data is rarely
possible, since only the probability of belonging
to one of the 4 types can be determined, d) the
ablation coefficient, sigma and the shape-density
coefficient, K, cannot be construed as a weighted
average and must be taken for each bolide type
separately, e) if other precise observational data
can be derived (e.g. data on heights and velocities
at several points), they are certainly preferable
for determining the sigma and K values. The
characteristic light curve determined for each of
these 4 meteoroid types will be presented.
PSB-10
Microwave Observations of Molecules in the Earth
Atmosphere during a Meteor Shower: The Leonids
Didier Despois et al. (Observatoire de Bordeaux,
INSU/CNRS, B.P. 89, F-33270 Floirac, France;
e-mail: despois@observ.u-bordeaux.fr)
Meteor showers affect to some extent the
chemical composition of the upper atmosphere. We
discuss the use of mm/submm wave spectroscopy to
study the molecules delivered or produced, some of
which may be of importance for prebiotic chemistry.
We present radio observations of the HCN line using
the CSO radio telescope in Hawaii on Nov. 18/19
1999 ; the night after the second Leonid shower
maximum showed unusually low HCN abundances above
45 km altitude, which are only recovered after
sunrise. New observations to test the link of the
HCN line variation with the meteor shower will be
undertaken for 2001 Leonids. PSA-37
Components of a New Interplanetary Meteoroid
Model
V. Dikarev (1, 4), E. Gruen (1), M. Landgraf
(2), J. Baggaley (3), D.P. Galligan (3)
1) Max-Planck-Institut für Kernphysik,
Heidelberg, Germany; 2) European Space Operations
Centre, Darmstadt, Germany; 3) University of
Canterbury, Christchurch, New Zealand; 4)
Astronomical Institute of St. Petersburg State
University, Russia
New populations of interplanetary dust are
proposed for the new ESA interplanetary meteoroid
model. Formulation of the model and its populations
differ from those adopted in earlier meteoroid
models and are tied to long-term dynamics of the
interplanetary dust. To validate the new model,
infrared emission observations with COBE DIRBE
instrument, impact counts with the dust detectors
aboard Galileo and Ulysses spacecraft, and the
radar meteors monitored with AMOR are used.
10.9
Hypervelocity Impact Effects on Spacecraft
Gerhard Drolshagen (ESA/ESTEC)
Every spacecraft in orbit is exposed to a
certain flux of impacting particulates. These
impacts occur at typical velocities between a few
and some tens of kilometers per second. Submicron
and micron sized particles can lead to a
degradation of sensitive spacecraft surfaces and
equipment, like mirrors, optical sensors and
thermal control surfaces. Somewhat larger particles
with diameters in the range of tens to hundreds of
microns can penetrate outer spacecraft coatings and
foils as well as solar cells. Penetration of solar
cells can lead to short circuits and subsequently
to a degradation of the power supply. Craters
resulting from hypervelocity impacts are typically
3-20 times larger (depending on the material and
impact parameters) then the impactor. That implies
that even submillimeter sized particles can cause
problems for sensors and for the future use of
impacted surfaces (e.g. sealing, Shuttle windows).
In addition to these mechanical effects, every
hypervelocity impact creates an impact plasma. Such
an impact generated plasma can lead to
electromagnetic interference with spacecraft
systems and payloads. More importantly, the impact
plasma can also trigger a discharge of
electrostatically charged dielectric surfaces,
releasing a current which is much larger than what
would be possible by the impact alone. Millimeter
sized particles can penetrate exposed tanks and
seriously damage certain equipment. In addition the
momentum transfer can lead to attitude problems.
Impactors of cm size or larger will typically lead
to complete destruction of the impacted spacecraft
part. The presentation will give an overview of the
hypervelocity impact effects on spacecraft and also
briefly address some common protection measures.
9.1
[To top of page]
Persistent Leonid Meteor Trails: Types I and
II
J.D. Drummond, S. Milster, B. W. Grime, D.
Barnaby (Air Force Research Laboratory), C. S.
Gardner, A. Z. Liu, X. Chu (University of
Illinois), M. C. Kelley, C. Kruschwitz (Cornell
University) and T. J. Kane (Pennsylvania State
University)
From our 1998 and 1999 study of Leonid lingering
trails, we have identified two types of trails.
Type I trails are wide (1 km after a minute) with
high diffusion rates (1000 m2/sec), appear turbid,
optically thick, and 'puffy'. Type II trails are
narrow (< 100 m), often parallel, with low
diffusion rates (10 m2/sec), appearing optically
thin, smooth, and clean. Of the four trails
extensively studied, one is Type I only, another is
Type II only, and two show both types of trails.
Information (especially altitude) from a sodium
lidar is used to derive detailed geometric
parameters for the trails. For example, diffusion
appears to be a function of altitude, with the
hyperbolic tangent function describing the
transition from low to high rates. A 17 minute
video will be shown, and line emission rates,
diffusion coefficients, and other data will be
given for each. PSA-23
Meteor Trail Evolution: Comparison between
ALTAIR Radar Observations and Plasma
Simulations
Lars Dyrud, Meers Oppenheim, Sigrid Close,
Stephen Hunt, Axel vom Endt and Kelley Mc Millon
(Center for Space Physics, Boston University, 725
Commonwealth Ave, Boston, MA 02215, USA)
We present the first direct comparisons between
plasma simulations and radar observations to
explain the the most salient features of
non-specular meteor trail echos. The radar
observations were obtained during Leonids 1998 with
the highly sensitive ALTAIR radar in the Kwajelein
Atoll. Plasma simulations demonstrate that meteor
trails are unstable to growth of gradient-drift
Farley-Buneman (GDFB) waves that become turbulent
and generate large B-field aligned irregularities
(FAI). These results indicate that the non-specular
echos, that can extend between 5-10 km in altitude
range, are reflections from plasma instability
generated FAI. The simulation results can explain a
number of characteristics of these non-specular
observations. The observed altitudinal extent of
the trail echos. Trail diffusion in the plane
perpendicular to B that can be up to an order of
magnitude larger than expected from ambipolar
diffusion. echos. Additionally, meteor and
atmospheric properties including neutral
temperature, neutral-ion collision frequency, and
meteoric ion mass may be inferred with greater
accuracy then previously possible. 7.6
Comparison of Meteoroid and Space Debris Fluxes
to Spacecraft in Earth Orbit
Veronika Ekstrand and Gerard
Drolshagen(ESA/ESTEC)
Spacecraft in earth orbit will be impacted by
natural meteoroids and man-made space debris
particles. The relative ratio depends mainly on the
spacecraft orbit and attitude. Predicted number of
impacts from different flux models will be
presented for particle sizes ranging from microns
to cm. For low Earth orbits meteoroid fluxes
dominate for sizes between some tens of microns and
about 1mm while space debris is more abundant for
smaller and larger sizes. The mode differences for
a given population indicate the present level of
uncertainty. 9.4
The Effective Diffusion Coefficient of Meteor
Trails above 100 km
W.G. Elford (Department of Physics and
Mathematical Physics, University of Adelaide,
Adelaide 5005, Australia) and M.T. Elford (Atomic
and Molecular Physics Labs., Res. School of
Physical Sciences and Eng., Australian National
University, Canberra, 0200, Australia)
In a recent paper R E Robson [Phys Rev E, 63
(2) 026404, 2001] has set the problem of the
diffusion of meteor trails "in the context of
mainstream plasma physics". The outcome is a new
expression for the amplitude of the scattered radar
signal from an underdense trail, viz.,A(t) = A(0)
exp[-4k¬* tDeff] where Deff = Dll
sin¬*m sin¬*q + D^(1- sin¬*m
sin¬*q ) . Dll and D^ are the ambipolar
diffusion coefficients parallel and perpendicular
to the magnetic field, q is the angle the field
makes with the trail, and m is the angle between
the wave vector and the normal to the plane of the
trail and the field. Further, the two diffusion
coefficients are simply related by the expression
D^ = Dll (1+r )-1, where r depends on the cyclotron
and collision frequencies of the electrons and
ions. Using laboratory based data for the values of
the parallel diffusion coefficient and the
collision frequencies, values of the effective
diffusion coefficient have been calculated for
radar observations of underdense trails as a
function of trail orientation (radiant position)
and reflection point heights. Dramatic reduction of
the effective diffusion coefficient of high
altitude trails (>110 km) occurs when the radar
beam is directed orthogonal to the magnetic field.
The new values are applied to several sites of
meteor radars. 5.4
Effects of Meteoroid Fragmentation on Radar
Observations of Meteor Trails
W.G. Elford and L. Campbell (Department of
Physics and Mathematical Physics, University of
Adelaide, Adelaide 5005, Australia)
The majority of radar echoes from meteor trails
do not show the Fresnel diffraction oscillations
expected to occur just after the ablating meteoroid
passes the point on the trail where the orthogonal
from the radar station intersects the trail. For 50
years this has been attributed to fragmentation of
the meteoroid prior to or during the ablation
phase. However, direct evidence of fragmentation
from radar studies has been almost non-existent.
Recently, a breakthrough has occurred on two
fronts, (a) observations of amplitude oscillations
in down the beam meteor echoes, and (b) deduction
of the structure of meteor trails using radio
holography. In this paper plausible models to
explain the new observations will be presented and
applied to the question of the degree of
fragmentation required to explain the paucity of
Fresnel diffraction oscillations. Also, other new
evidence of fragmentation will be presented.
PSB-2
Observations of the Structure of Meteor Trails
at Radio Wavelengths Using Fresnel Holography
W.G. Elford (Department of Physics and
Mathematical Physics, University of Adelaide,
Adelaide 5005, Australia)
Radar observations of a meteor trail are the
temporal variations in the amplitude and phase of
the scattered radio signal usually recorded at one
site. During the formation of the trail in the
radar beam the recorded received signal can be
considered as a one-dimensional diffraction pattern
produced by a moving source. This diffraction data
contains information on the structure of the trail
that can be revealed by an appropriate Fresnel
Transform. An analytical technique for carrying out
this transform of meteor radar data will be
described and examples given of the outcomes for a
range of typical diffraction data. Inherent in the
outcomes are refinements in the value of the speed
of the meteoroid, the presence of multiple sources
(presumed due to fragmentation) and a measure of
the lateral motion of the trail during formation
due to wind drift. 6.5
[To top of page]
Radar Meteor Observations at 2 MHz
S. I. Grant and W.G. Elford (Department of
Physics and Mathematical Physics, University of
Adelaide, Adelaide 5005, Australia)
The Buckland Park MF radar ( 34 S, 138 N ),
located near Adelaide, Australia has been used for
night time meteor observations. Distributions of
meteor heights and incoming speeds have been
determined from observations over selected periods
during 1999 and 2000. Most radar meteor
observations are conducted using VHF radars, with
the wavelength-dependent meteor echo ceiling
limiting observation to heights below about 110 km.
In contrast MF radars have the potential to make
observations to heights exceeding 140 km, and hence
provide information on any high altitude component
that contributes to the meteor true height
distribution. A significant limiting factor
affecting such observations is the presence and
strength of the night time E-region. PSB-3
Resonance Structure of Meteoroid Streams
V.V. Emel'yanenko (South Ural University,
Russia)
The dynamical behaviour of meteoroid streams is
studied on the basis of the resonance theory of
perturbations. Parameters are calculated for the
principal resonance zones near the orbits of the
main meteoroid streams. The features of changes in
the spatial number density for librating,
circulating and stochastic-type motion are
described. In the case of librations near centres
of resonances, the density of meteoroid streams
changes almost periodically, and resonant particles
produce compact trails. On the other hand, the
stochastic motion of meteoroid streams is similar
to that of a diffusion process. The Leonid, Lyrid,
Ursid, Perseid and Bootid outbursts as indicators
of the described dynamical features are discussed.
Recommendations are given for the future
observations of the annual meteor showers. 1.7
Meteor Head Echo Observations Using the
Millstone Hill/MIDAS-W UHF Incoherent Scatter Radar
System
Philip J. Erickson and Frank D. Lind
(Atmospheric Sciences Group, MIT Haystack
Observatory)
UHF incoherent scatter radars can study meteor
influx into the upper atmosphere through recording
so-called meteor head echoes, which result from
scattering of the incident wave from structures
surrounding an inbound meteor as it ablates in the
80 &emdash; 120 km altitude range. The Millstone
Hill 440 MHz incoherent scatter radar, with its
associated 68 m zenith and 46 m steerable antennas
and 2.5 MW peak power transmitter, was used as
early as 1962 in observations leading to a seminal
series of papers by John Evans describing UHF
meteor scattering characteristics. Recently, we
have employed the Millstone system, using a
prototype wideband data acquisition system
(MIDAS-W) and a Barker code transmission scheme
similar to work done at EISCAT, in a series of head
echo detection experiments during the Leonid meteor
showers of November 1999 and November 2000. We
describe the capabilities of the MIDAS-W system for
meteor research, and present selected results of
these Leonid observations along with future plans.
7.5
Capture of Meteoroids by Aerogel Exposed on the
MIR
G. Ferrini and L. Colangeli (Osservatorio
Astronomico di Capodimonte, Napoli), P. Palumbo
(Istituto Universitario Navale, Napoli), A.J.
Westphal (Space Sciences Laboratory, University of
California at Berkeley) and J. Borg (Institut
d'Astrophysique Spatiale, Université Paris
Sud)
The Earth orbit environment is an ideal place
for the collection of meteoroids of different
origins. The intact capture of these solid
particles in space is of special interest for
cosmic dust research in order to understand their
nature, to assure the complete characterisation of
their chemical composition and to determine their
orbits and relative contribution to the total flux
in the Solar System. Searching for these results,
in the last few years a number of experiments were
carried out in Low Earth Orbit, many of which
onboard the Russian MIR Space Station. The COMET-99
experiment flew on the MIR between November 1998
and April 1999, during Earth encounter with
Leonids. With the aim of in situ collection of
particles from this meteor stream, a package
composed of different dust collectors, belonging to
various capture experiments, was exposed to space.
Among these collectors, two blocks of silica
aerogel provided by the Cosmic Physics Laboratory
of Napoli were included. Laboratory analyses on
these aerogels show a conspicuous presence of
tracks and captured solid particles. Here we
present our results on the extraction and analysis
of collected grains. 9.3
[To top of page]
On the Atmospheric Dynamics of the Tunguska
Cosmic Body (Dedicated to P. Farinella)
L. Foschini (1), Ch. Froeschlé (2), R.
Gonczi (2), T.J. Jopek (3), G. Longo (4) and P.
Michel (2)
1) Istituto TeSRE &emdash; CNR, Bologna, Italy;
2) Observatoire de la Cote d'Azur, Nice, France; 3)
Obserwatorium Astronomiczne Universytetu A.
Mickiewicza, Poznan, Poland; 4) Dipartimento di
Fisica, Università di Bologna &emdash; INFN
Sezione di Bologna, Italy.
We studied the available scientific literature
on the Tunguska event of 30 June 1908 in order to
extract a sample of data from which we calculate
the possible parameters of the atmospheric dynamics
of the Tunguska Cosmic Body. We perform a
comparative analysis by means of some of actual
theoretical models and with the help of
interplanetary dynamics, to exclude unphysical
orbits. From the obtained results, the probability
that the TCB was an asteroid is very high.
PSA-34
The Leonid Meteors Found in Chinese Historical
Records
Y. Fujiwara (Nippon Meteor Society)
Beijin Observatory published the compilation of
the Chinese historical records of meteor showers
and individual fireballs. Since some records of the
fireballs indicate the meteor trail with Chinese
constellation or bright fixed stars and the
directions of the path, we can estimate probable
path of the meteor. So we can identify the
permanent shower meteor not only the aid of the
solar longitude at the meteor apparition but also
the its path. In this paper some Leonid meteor
records found in Chinese chronicles by using this
method are presented. PSA-21
TV Observation of the 1998 Giacobinid Meteor
Shower in Japan
Y. Fujiwara, M. Ueda, M. Sugimoto and T.
Sagayama (Nippon Meteor Society), M. Satake and A.
Furoue (Kansai Astronomical Society)
Activity of Giacobinid (Draconid) meteor shower
was recognized on October 8th, 1998, in Japan, with
multi-station TV observations. 104 Giacobinid
meteors have been recorded, and among which precise
orbit could be determined for 60 meteors. It is
found that the radiant points were concentrated
compactly. Furthermore, the beginning heights of
Giacobinid meteors are significantly higher than
typical TV meteors with similar velocities.
PSA-11
Probing the Structure of the Interplanetary Dust
Cloud Using the AMOR Meteoroid Orbit Radar
David Galligan and Jack Baggaley (University of
Canterbury, Christchurch, New Zealand)
During the past five years the University of
Canterbury's (New Zealand) Advanced Meteor Orbit
Radar (AMOR) has catalogued over half a million
high-quality meteoroid orbits. This data set, which
is greater in size than the combined total of all
previous surveys, provides high resolution
information on the structure of the dust cloud
orbiting the Sun. It is important to be able to
obtain an astronomically true picture of this dust
population for inclusion in interplanetary dust
models, as a background to studies of interstellar
dust such as that detected recently by W.J.
Baggaley, and from a general scientific interest
point of view. There are a series of selection
effects which must be allowed for in changing from
the orbital distributions as observed directly to
"true" distributions in space &emdash; these
effects, and the "corrected" distributions
resulting from their removal, will be discussed.
10.3
Io Revealed in the Jovian Dust Streams
Amara L. Graps (1), Eberhard Gruen (1), Harald
Krueger (1), Mihaly Horanyi (2), Håkan
Svedhem (3) and the Galileo and Cassini Dust
Science Teams
1) Max-Planck-Institut für Kernphysik,
Heidelberg, Germany; 2) LASP, Boulder, USA; 3)
European Space Research and Technology Centre,
Noordwijk,The Netherlands
The Jovian dust streams are high-rate (at least
250 km/s) bursts of submicron-sized particles
travelling in the same direction from a source in
the Jovian system. The source of the Jovian dust
streams is Jupiter's moon, Io, in particular, dust
from Io's volcanoes. Charged Io dust, travelling on
trajectories from Io's location, is shown to have
some particular signatures in real space, in
frequency space, inside of Jupiter's magnetosphere,
and outside of Jupiter's magnetosphere. The work
presented here describes an emerging
electrodynamical picture of the Jovian dust streams
as they appear inside and outside of the Jupiter
environment using data from the Galileo spacecraft
in years 1996-2000 and from the Galileo-Cassini
December 2000 dust stream measurements. We show
that some aspects of the dust stream particles'
dynamics in real space can be understood if the
particles charges are a varying parameter in the
force equation. The Jovian dust stream dynamics in
the frequency-transformed Galileo dust measurements
show two different signatures, depending whether
the dust detector is located outside of the Jovian
magnetosphere or inside of the Jovian
magnetosphere. This time-frequency analysis is the
first direct evidence that Io is the source of the
Jovian dust streams. 10.8
Dust Astronomy
Eberhard Gruen (MPI-Kernphysik, Heidelberg)
Dust particles, like photons, are born at remote
sites in space and time, and carry from there
information that may not be accessible to direct
investigation. From knowledge of the dust
particles' birthplace and the particles' bulk
properties, we can learn about the remote
environment out of which the particles were formed.
This approach is called dust astronomy which is
carried out by means of dust telescopes on dust
observatories in space. Targets for dust telescopes
are dust from the local interstellar medium, meteor
stream dust, cometary, asteroidal, and lunar dust,
and space debris. Dust particles' trajectories are
determined by in-situ dust detectors with narrow
apertures and by the measurements of the electric
charge signals that are induced when the charged
grains fly through appropriately configured grid
systems. Modern in-situ dust detectors are capable
of providing mass, speed, physical and chemical
information of dust grains in space. A "dust
telescope" can, therefore, be considered as a
combination of detectors for dust particle
trajectories along with detectors for physical and
chemical analysis of dust particles. A
state-of-the-art dust telescope will consist of an
array of parallel-mounted dust instruments, which
share a common impact plane of at least one square
meter in size. 11.5
[To top of page]
Porous Flake Meteoroids and the Structure of
Small Bodies in the Solar System
B. Gustafson (Laboratory for Astrophysics,
Department of Astronomy, University of Florida,
Gainesville, Fl 32611, USA;
gustaf@astro.ufl.edu)
There is significant evidence that comets and
even some asteroids preserve in the structure of
their materials the physical dimensions of the
interstellar dust grains that they were made from.
Laboratory simulations of comet material in the
form of colloidal grains of a narrow size
distribution embedded in water ice produced thin
flakes from the process of sublimation. Simple
calculations show how the gas pressure below a
grain on the surface of a sublimating material
increases sharply as the layer of grains grows from
a monolayer to becoming two particles thick. This
is the probable cause for the formation of thin
flakes in the experiment and also on the surface of
comets under some circumstances. It probably
corresponds to one of several modes of dust and
meteoroid production from comets. I will review
some evidence for the presence of such flake-like
structures among dust and meteoroids. From the
external shape of dust aggregates, we will now turn
our attention to the internal structure of grain
arrangement. I will show how optical grain
properties including colour and polarization is
evidence for a hierarchy in the arrangement that
may be indicative of turbulence in the nebula at
the time of aggregation.. 10.1
Development of a New Reflectron Type TOF Mass
Spectrometer for Dust Analysis in Space
Yoshimi Hamabe (1), Sho Sasaki (1), Hideo Ohashi
(2), Tohru Kawamura (3), Ken-ichi Nogami 3), Hajime
Yano (4), Sunao Hasegawa (4), and Hiromi Shibata
(5)
1) Department of Earth and Planetary Science,
University of Tokyo; 2) Department of Ocean
Science, Tokyo University of Fisheries; 3)
Department of Physics, Dokkyo University School of
Medicine; 4) Institute of Space and Astronautical
Science; 5) High Fluence Irradiation Facility,
University of Tokyo
In order to analyze the elements of dust
particles in space, we have been developing a
reflectron-type dust TOF-MS (Time-Of-Flight Mass
Spectrometer) with a curved electric field. Now we
have done performance experiments of our device by
impacting hypervelocity microparticles with a Van
de Graaff accelerator at HIT (High Fluence
Irradiation Facility, University of Tokyo), where
carbon particles of 0.3-2.0 micrometer in diameter
are accelerated up to 5-20 km/s which is compared
to the velocity of dust particles in space. The
results showed the device has higher mass
resolution than the system with a parallel
reflecting region under the same experiment
situation by factor 2 or 3. Moreover the TOF
spectra showed the higher detection efficiency, and
the value was 10 times higher compared to the
parallel reflectron TOF-MS. These effective results
are considered to be caused by a curved electric
field in a reflecting region. PSB-18
Millimeter Continuum Observations of Parent
Comets of Meteor Storms
Hitoshi Hasegawa (ASTEC, Inc.), Nobuharu Ukita
(Nobeyama Radio Observatory) and Ryosuke Nakamura
(NASDA)
The 2 millimeter continuum observations of
parent comets of meter storms, P/Tempel-Tuttle and
P/Giacobini-Zinner, were made with a bolometer
array installed on the 45m radio telescope at the
Nobeyama Radio Observatory. P/Tempel-Tuttle was
observed on January 16, 1998, near its closest
approach to the earth, and P/Giacobini-Zinner was
observed November 5 and 8, 1998. The maps obtained
showed no signal from these comets greater than
12.0 mJy for P/Tempel-Tuttle and 17.4 mJy for
P/Giacobini-Zinner (3 sigma). Using the same
assumptions in Jewitt and Mathews (1997, AJ, 113,
1145), we estimated that the mass upper limits in
the 12 arcsec beam were 7.5E9 kg and 6.2E10 kg for
P/Tempel-Tuttle and P/Giacobini-Zinner
respectively. We esitimated total mass of these
meteor streams form the observed upper limits. The
derived total mass upper limits are serveral orders
larger than those expected from meteor
observations. 1.2
Parent Objects of Alpha Capricornid Meteor
Stream
Ichiro Hasegawa
The complex structures of Alpha Capricornid
stream are investigated from about 45 photographic
meteors observed during July 8 and September 10.
Although there are several subgroups in this
stream, it is confirmed that the main parent comet
is 45P/Honda-Mrkos-Pajdusakova.
72P/Denning-Fujikawa and 141P/Machholz 2 are likely
to be additional parent comets. Near earth objects,
(2101)Adonis and (9162)1987 OA are also suggested
as the possible parent objects. 1.9
High Resolution Meteor Light Curve
Investigations
R.L. Hawkes, J.E. Bussey, S.L. MacPhee, C.S.
Pollock and LW. Taggart (Physics Department, Mount
Allison University, Sackville, NB Canada E4L
1E6)
The dustball model of meteoroid structure would
be expected to lead to short duration fluctuations
on light curves, anomalous decelerations, and
possibly light production over a significant
spatial region. Traditional approaches to meteor
light curve video analysis have not used all of the
information which is provided by the CCD video
signal. We have employed coincidence and
correlation analysis using two spatially separated
microchannel plate (Gen III) image intensified CCD
observations systems coupled to digital video
recording equipment to search for fine scale
structure both perpendicular to the line of motion
and along the meteor path and attempted
deceleration measures. We will describe the digital
image analysis approaches, give some model
predictions, as well as preliminary results.
3.8
Sondrestrom ISR Meteor Measurements
C.J. Heinselman and J. Jørgensen (SRI
International, 333 Ravenswood Ave, Menlo Park, CA
94025, USA)
Measurements of the meteoric phenomena with the
Sondrestrom ISR at 1290 MHz have previously been
limited to studies of sporadic E layers and their
relationship to infrequent, strong meteor echoes.
Recent enhancements to the Sondrestrom data
acquisition system have enabled the development of
data collection codes better suited to probing the
meteor head echo phenomena at this frequency.
Initial results will be presented of measurements
from recent meteor showers. Future plans will also
be discussed for making more routine meteor
measurements with the Sondrestrom system. 7.8
Two-frequency Meteor Observations Using
ALTAIR
Stephen Hunt and Sigrid Close (MIT Lincoln
Laboratory, 244 Wood Street, Lexington MA, 02173,
USA)
We present a sample of radar meteors detected
during the November 1998 Leonid shower that were
collected using the ARPA Long Range Tracking and
Instrumentation Radar (ALTAIR). A total of 29
minutes of VHF data were collected near the peak of
the shower, which produced over 900 head echoes; 17
minutes of simultaneous UHF data were collected,
which resulted in over 500 head echoes. These data
were analyzed to determine frequency-dependent
radar cross section and shape characteristics. In
addition, the azimuth and elevation data were used
to compute the true velocity and deceleration of
the head echoes, which produced the result that a
meteoroid's deceleration is not constant. Finally,
the first head echo that was detected using three
frequencies (160 MHz, 422 MHz, 1320 MHz) is
discussed.
ALTAIR is a highly sensitive, two-frequency
radar that is uniquely suited for detecting meteor
head echoes. ALTAIR transmits right circular
polarized energy and records both left circular and
right circular data, as well as azimuth and
elevation difference channel data. These data allow
the accurate determination of a target's position,
velocity and deceleration. ALTAIR's system
sensitivity allows the reliable detection of a -55
dBsm target in VHF and a -75 dBsm target at UHF at
a range of 100 km. 7.4
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Arecibo Detection of a "Large" Mass Component in
the Ulysses Interstellar Dust Flow
David Meisel (1, 2), Diego Janches (2, 3) and
John Mathews (2)
1) SUNY-Geneseo; 2) CSSL-PSU; 3) Swedish
Institute of Space Physics, Kiruna, Sweden;
diego.janches@irf.se
Micrometeoroids detected with the Arecibo UHF
radar have hyperbolic heliocentric velocities as
well as measurable atmospheric drag decelerations.
Thus both orbits and sizes can be inferred.
Evidence is presented for the discovery of a large
size (10 microns> radius >0.2 micron)
component of the Ulysses interstellar particle
flow. The mean velocity of these "large" particles
is somewhat higher than for the mean of the Ulysses
particles themselves, but when the Arecibo particle
velocity vectors are transformed to system moving
at their average velocity, good coincidence with
the Ulysses radiant is found. Larger extrasolar
particles (>10 microns radius) have been
detected, but they do not correlate well with the
Ulysses radiant. PSB-21
The Size Distribution of Arecibo ISPs and its
Implications
David Meisel (1, 2), Diego Janches (2, 3) and
John Mathews (2)
1) SUNY-Geneseo; 2) CSSL-PSU; 3) Swedish
Institute of Space Physics, Kiruna, Sweden;
diego.janches@irf.se
Extrasolar particles observed at Arecibo and
deemed to be true interstellar particles display a
lognormal distribution of sizes. The radii also
correlate with their original hyperbolic, solar
system impact parameters. The upper end of the
observed distribution occurs for particles on the
order of 10 microns radius, while the lower end of
the observed distribution occurs for particles ten
times smaller. Such a distribution is
characteristic of a "breakage" process (Wadsworth,
1990) and has been shaped by various creation and
loss processes during transit from their source
regions to the earth. The observed size limits
agree quite well with models attempting to explain
Ulysses spacecraft observations. 11.7
Tristatic measurements of meteors using the 930
MHz EISCAT radar system
Diego Janches (1, 2), Asta Pellinen-Wannberg
(1), Gudmund Wannberg (3), Assar Westman (3) and
Ingemar Häggström (3)
1) Swedish Institute of Space Physics, Box 812,
SE-981-28, Kiruna, Sweden; 2) Communication and
Space Sciences Lab, Penn State University,
University Park, PA, 16802, USA; 3) EISCAT
Scientific Association, Box 164, SE-981 23, Kiruna,
Sweden
We report results from the first tristatic
measurements of radar meteors obtained during
November 17-18, 1997 and 1998, using the UHF (930
MHz) EISCAT radar system. This system consists of
three antennas located in Tromso, Norway (69.6 N;
19.2 E); Kiruna, Sweden (67.9 N; 20.4 E) and
Sodankyla, Finland (67.4 N; 26.6 E). Since EISCAT
observes mostly head-echoes, a general
characteristic of high power/large aperture radars,
very precise Doppler velocity determination are
possible. In addition using the technique reported
here, absolute geocentric meteor velocity and
precise radiant information are deduced for those
meteors that are detected simultaneously by all
three receivers. An overview of the methodology and
a summary of the results obtained so far are
reported in this work. To the best of our
knowledge, these observations represent the first
of their kind and prove EISCAT to be a crucial
instrument for the study of extraterrestrial
particles entering the earth's atmosphere, in
particular at very high geocentric latitudes.
7.7
Leonid Storm Research in the Near Future
P. Jenniskens (SETI Institute, at NASA Ames
Research Center)
Recent observations and dynamical models show
that the biggest Leonid storms in this season are
still to come. In November of 2001 and 2002, Zenith
Hourly Rates are predicted to increase to levels
above the storm of 1999. And the next storm is not
until 2099. Results from the 1999 Leonid storm
research were published, recently, in special
issues of Earth, Moon and Planets, Meteoritics
& Planetary Science, and Geophysical Research
Letters. In this presentation, I will summarize
some results from key areas of Leonid storm and
meteor outburst research to date, elaborate on how
those results further other research fields, and
discuss in what areas future research might make
rapid progress. PSA-13
Meteors: A Delivery Mechanism of Organic Matter
to the Early Earth
P. Jenniskens (SETI Institute, at NASA Ames
Research Center), C.O. Laux, D. Packan and C.H.
Krueger (Stanford University), I. Boyd (University
of Michigan, Ann Arbor) and O.P. Popova (Institute
for Dynamics of the Geospheres RAS, Moscow)
All potential exogenous pre-biotic matter
arrived to Earth by way of our atmosphere, where
much material was ablated during a luminous phase
called "meteors" in rarefied flows of high (up to
270) Mach number. The recent Leonid showers offered
a first glimpse into the elusive physical
conditions of the ablation process and atmospheric
chemistry associated with high-speed meteors, and
the possible pathways of survival for meteoric
organic compounds and the creation of reduced
carbon compounds through aerothermochemistry. In
this presentation, I will discuss the role that
meteors can have played in delivering organic
matter to the early Earth as precursors for the
origin of life. 3.3
The 2000 Ursid Shower Prediction and
Observations
P. Jenniskens (SETI Institute, at NASA Ames
Research Center) and E. Lyytinen (Finland)
We applied Leonid dynamical models to
Halley-type comet 8P/Tuttle and its meteor shower,
the Ursids. An outburst was predicted for December
22, 2000, when Earth was to cross the dust trails
that originated during the 1392 and 1405 returns.
An announcement was made in the IAU circulars and
in extended form in WGN, the Journal of IMO. The
meteor outburst observed from California using
video and photographic techniques. At the same
time, five Global-MS-Net stations in Finland, Japan
and Belgium counted meteors using forward meteor
scatter. We can now confirm the return of the Ursid
outburst with a maximum at 8:06±07 UT,
December 22nd, when activity peaked at ZHR ~ 90.
The Ursid rates were above half peak intensity
during 4.2 hours. The relative contribution from
both dust trails to the outburst is discussed, as
is the relevancy of this for future meteor outburst
forecasts. PSA-3
[To top of page]
A Physical Model of the Sporadic Meteoroid
Complex
J. Jones, M. Campbell and S. Nikolova
(Department of Physics and Astronomy, University of
Western Ontario, London, Ontario, N6A 3K7
Canada)
Almost a half century ago Davies (1957) and
Hawkins and Southworth (1958) showed that the
directional distribution of the trajectories of
sporadic meteoroids is not isotropic. More recently
Jones and Brown (1993) showed that there are six
main clusters of sporadic meteor radiants for which
they determined the mean directions and widths. In
this paper we present the results of a model of the
evolution of sporadic meteoroid orbits which takes
long and short-period comets as the sources of
meteoric material and the Poynting-Robertson effect
as the dominant mechanism of orbital change. The
predicted radiant and orbital distributions are in
excellent agreement with observation. It is shown
that the inclusion of Steel and Elford's (1985)
estimate of the collisional lifetime of
meteoroid-sized particles, yields the observed
variation of the volume density of the particles
with distance from the Sun. 10.4
Radar-meteor Velocity Determination
J. Jones, K. Ellis and M. Campbell. (Department
of Physics and Astronomy, University of Western
Ontario, London, ON, N6A 3K7 Canada)
Meteoroid velocities are essential for the
calculation of orbits. Most methods for measuring
radar-meteor velocities require high
signal-to-noise ratios and the question arises
whether the process of selecting those meteor
echoes suitable for velocity determination
introduces bias. For example, are fragmenting
meteors discriminated against because their Fresnel
oscillations are "washed out"? In this paper we
have examined the time-honored "rise-time" method
and tried to push it to its limit. Model
calculation indicated that an accuracy of 5% should
be attainable for signal-to-noise rations of 20 dB.
Simultaneous measurements using identical radars
operating at 29 MHz and 38 MHz yield an accuracy of
about 13% for echoes with signal-to-noise ratios
> 6dB. The method allows a velocity
determination for every echo. 6.2
The Computer Model "KAMET": A New Generation
Arkady Karpov, Sergey Tereshin and Joury
Abrosimov
In this work , we present the results of the
modernization of the computer model "KAMET".
"KAMET" contains the following primary software
modules: (1) astronomical model of the flux of
meteoric material into an atmosphere of the Earth;
(2) a block of geometrical aspect equations; (3)
the physical model; (4) the electrodynamics model;
(5) a block of power equations and (6) an
astronomical component of model "KAMET" is based on
long-term experimental radar observation which are
carried out on the meteoric radar of the Kazan
university. Modifiction of the radiotomography
input data gives us the possibility of taking into
account a thinner structure of meteor flux.
The astronomical model of inflow of meteoric
material into the atmosphere of the Earth is
expressed by tables of cumulative density of meteor
flux. Densities of meteor flux which are higher
than a given amount are obtained by analytical
recalculation of density above a given threshold of
detection as indicated by the experiment.
Subsequent calculations are reduced to some
characteristic height. It is an approximation with
an accuracy that is impossible to evaluate at
present.
We offer here a different simulation method
which allows one to decide a problem of
recalculation without reduction of the data to a
characteristic height. The simulation method also
allows revision of the tables of meteor flux
density for new physical models that may be
introduced. PSA-33
The Measurement to Ozone Concentration by Kazan
Radar Observations
Arkady Karpov, Alexey Naumov, Andrey Konnov,
Matvey Krimer
An indirect method of measurement of ozone
concentration based on duration of the radar
observed radiometeor reflections is presented. A
comparative analysis of different processes has
been carried out from recombinations &emdash;
radiative, and dissociative processes to
recombinations under triple collisions. The most
important role in such processes is dissociative
recombination and recombinations with the
electronic stabilization.
By means of "KAMET" computer model, we have
studied the disintegration of meteoric trails. The
modeling of reflection duration was carried out for
different mechanisms:
o Without accounting for recombinations;
o With accounting for only dissociative
recombinations;
o With accounting for recombinations with
electronic stabilization;
o With accounting for both mechanisms;
The model results are compared with experimental
durations of meteoric burst observed at a frequency
of 32,8 MHZ. PSA-35
Thin Space Structure of Meteor Flux
Irregularities in Large Meteor Showers in 1986
-1999
A.V. Karpov and E.Z. Yumagulov
Meteoric observations obtained with the radar
KGU-M5 (1986 &emdash; 2000), have been archived in
an Oracle 8 relational database. An advanced
statistical method of searching for fine spatial
structure of meteoric showers has been applied to
the database and information on the distribution of
material in the Quadrantid, Geminid and Perseid
showers has been obtained.
For the Geminid meteor shower, evidence of
grouping was found in 49 % of the intervals of
observation (similarly for the Quadrantid and
Perseid showers 39% and 63 % were obtained,
respectively.). The results also had a dependence
on signal level. Groupings were detected (a) in 79
% of cases only at low signal level, (b) in 17 % of
cases the groupings were detected at both high and
low levels detection, and (c) in 4 % of cases
groupings were found only at high signal levels and
they were absent at low levels. The prevalence of
groupings observed at low signal levels corresponds
qualitatively well to that of a Poisson model of
particle distribution. 1.5
Meteoroid Stream Impacts on the Moon:
Information of Duration of Seismograms
O.B. Khavroshkin and V.V. Tsyplakov (Schmidt
United Institute of Physics of the Earth, Russian
Academy of Sciences, B.Gruzinskaya 10, 123885
Moscow D242, Russia)
The seismograms of meteoroid stream impacts on
the Moon have brought important information about
inside structure of the Moon more years ago. This
work is a new attempt of using records of "Apollo"
seismic network for receiving further information
about dynamic processes on the Moon. The Nakamura
Catalogue is employed for research of these
problems. We have built up some histograms from
seismic data of Catalogue. The duration of impact
_imp in minutes was a general parameter for our
analysis. The impact duration was plotted on the
horizontal axe of histogram and sum number of
impacts _ni for every impact duration was plotted
on its vertical axe. In other words, these
histograms are the graphic images of relationships
between _ni and _imp. Following kinds of
functions_ni=_ni(_imp) are analysed: (1) one impact
of a meteoroid per Earth day; (2) two impacts per
day; (3) three impacts per day; (4) four-eight
impacts per day; functions (1)-(3) have been built
up only within 1974 year; function (4) has been
built up for every year within 1974-1977 and for
their sum also. Preliminary conclusions of
processing histograms is as follows: the increase
of energy of impact from (1) to (3) moves a maximum
of histograms to shorter duration, especially it is
evident in the case of 4-8 impacts per day; every
histogram contains significant picks which are
58-56; 40; 38; 25; 19-20; 16 minutes, but 6; 10,13
minute picks are existed only for 4-8 imp/day
histogram. We expect that physical models for
explaining these picks might be discuses in the
meeting. 1.3
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Radioseismology as a New Method of
Investigations of Meteor Streams on the Moon and
Planets
A.A. Berezhnoi (1), E. Bervalds (2), O.B.
Khavroshkin (3) and G. Ozolins (2).
(1) Sternberg Astronomical Institute, Moscow,
Russia, (2) Ventspils International Radio Astronomy
Center, Riga, Latvia, (3) Institute of Earth
Physics, Moscow, Russia
Radioseismology is based on registration and
interpretation of radio emission of seismic origin.
Such radioseismic processes occur on the Moon,
planets, and asteroids. Non-thermal radio emission
of the Moon caused by rock fracturing, seismic
activity, and thermal cracking of the regolith was
detected during observations of the Moon at the 64
m Kaliazin radio telescope at 13 and 21 cm on July
31, 1999. We observed the Moon on November 16-18,
2000 with the 32 m Ventspils antenna at 25 mm.
During the morning of November 17 we registered
significant quasiperiodic oscillations of the lunar
radio emission starting near 1:44 UT and contining
until the end of observations at 7:17 UT.
Oscillations were also registered on November 18
starting near 2:28 UT. Intensive oscillations were
registered until about 7:00 UT with bottom to peak
heights of 5-10 K. The time of maxima of
oscillations does not contradict theoretical
predictions about the existence of three maxima of
the Leonid meteor shower on the Moon. Amplitudes of
oscillations were equal to 1-2 K before and after
the time of Leonid's maxima. These results can be
explained as the detection of lunar radio emission
of seismic origin caused by meteoroid impacts. The
implications of the radioseismic method for
determination of the intensity of meteor showers on
the Moon and planets and the internal structure of
the Moon are described. PSA-16
Temporal Structure of Meteoroid Stream and Lunar
Seismicity According to Nakamura's Katalog
O.B. Khavroshkin and V.V. Tsyplakov (Schmidt
United Institute of Physics of the Earth, Russian
Academy of Sciences, B.Gruzinskaya 10, 123885
Moscow D242, Russia)
Nakamura and Oberst pioneered in receiving data
of clustering of meteoroid streams from impact
seismograms. As a continuation of their research we
have derived some types of temporal series. Two
series 1 and 7 years in persistence (1974 and
1969-1977) are the temporal sequences of sum
numbers of impacts per unit time (one day, three
days). The third series one year in persistence
(1974) is the temporal sequence of impact events
and time intervals between them according to
Catalogue. We adopted that event amplitudes are
equal to unit. The duration of these events was
obtained from impact seismograms. The forth series
with the same persistence (1974) is the temporal
sequence of values equal to duration of impacts
averaged through day. All series were studied by
spectral analysis and as a result, common
periodicity for all series and supplementary picks
in only two series were obtained. Spectrum of the
series (1969-1977) disclosed time picks on Mercury,
Venus and Earth orbital periodicity (88; 115; 225;
365, 27.3 days). Comparative analysis of spectra
for other series disclosed following periodicity
picks: 44; 27; 5,5; 3,7 (for first series 1974 in
persistence); 10; 5; 3; 2.5; 2.23 days (for third
series); 10; 5; 3,3; 2.5; 2,23 days (for forth
series). The 10 and 5-days picks are exceptionally
interesting, because magnetic solar storms have the
same periodicity. The dust component of meteoroid
streams similar to dust plasma probably is
modulated by variation of solar magnetic fields.
Thin temporal structure of temporal variation of
meteoroid streams has the picks which coincide with
half-periods of neighbourhood binary star systems (
2.2 day &emdash; UWCma; 3.6 days &emdash; hAql).
PSA-6
Properties of Interstellar Dust Derived From
In-Situ Measurements and Extinction
Observations
Hiroshi Kimura and Ingrid Mann
Already since the 1930s observations of the
extinction of stellar radiation have revealed the
presence of dust in interstellar space. The
spectral variation of the interstellar extinction
was classically used to infer the size and
composition of interstellar dust along the line of
sight of observations. Current models also apply
measurements of elemental abundances in
interstellar space to place constraints on the dust
compositions. During the past decade, interstellar
dust particles that enter the solar system have
been identified with in situ measurements from
spacecraft. Analyses of these in-situ data provide
information on the properties of dust in the local
interstellar cloud, in which the solar system is
embedded. In this review, we first discuss problems
with current models when compared to the
experimental results and laboratory analyses of
presolar grains. We present an update on the status
of our modeling, in which the properties of
interstellar dust are consistent with astronomical
observations and in-situ experiments. We finally
discuss possibilities for future studies and
in-situ measurements. 11.2
Interstellar Particle Detection and Selection
Criteria of the Meteor Streams
B.L. Kashcheev and S.V. Kolomiyets (Kharkiv
State Technical University of Radioelectronics,
Lenin av., 14, Kharkiv, 61166, Ukraine)
There is a hypothesis on possible exposure of
interstellar particles from kinematics discussions.
If interstellar meteors are present among the
observed meteoroids with hyperbolic orbits, then
their heliocentric velocity distribution must
correspond to distribution of radial velocities of
close stars Thus, heliocentric velocity of
interstellar meteoroids equals to 46.6 km/sec.
Moreover, a concentration of meteor radiants to the
apex of the Sun should be observed for interstellar
meteoroids. In the paper there has been examined
probable distribution of number of interstellar
meteoroids. By appraisals of Belkovich O. I.,
Potapov I. N., 1985, Kazantsev A. M., 1998, the nor
less than 75% of interstellar particles which are
observed on the Earth are distributed in the
interval from 1 to 1,1. This interval of the
eccentricity is typical the eccentricity and for
orbits which have become hyperbolic because of
errors of their definition. The same the
eccentricity will belong to orbits of meteor
bodies, which have become hyperbolic because of
narrow rapprochement with planets. It is
investigated the opportunity of division the
observation orbital radiometeor data, with the
eccentricity, which exceeds one, according to
mechanism of their formation with the goal of
search the orbits of interstellar particles. They
are adduced the results of search the orbits of
interstellar particles by criterions which are
based on analysis of orbital elements and on
limitations which associates with conditions of
observation such particles on the Earth. The
eccentricity of 2303 investigated hyperbolic orbits
is in the interval from 1 to 2. The approbation of
search were made on the different samples from
observation material, which volume is more than 7
thousands hyperbolic and about parabolic orbits of
unique Kharkiv electronic catalogue 160000 orbits
of radiometeors to +12 starry size that were
registered in 1972-1978 years. 111 meteoroid
hyperbolic orbits with 1<e<2 were foundduring
21 March, 20 days before and 20 days after this
date (data for 1972-1978). Distribution of their
parameters is given. It is possible that there is a
certain number of interstellar meteoroids. 11.4
Extreme Beginning Heights for Non-Leonid
Meteors
Pavel Koten, Pavel Spurny, Jiri Borovicka and
Rostislav Stork (Astronomical Institute, Academy of
Science, Ondrejov Observatory, 251 65 Ondrejov,
Czech Republic)
Extreme beginning heights up to 200 km were
recently discovered for bright Leonid meteors. Here
we report results of the search among our
double-station video data of other meteor showers.
We found two eta-Aquarid and one Perseid meteors
with beginning heights up to 150 km and one Lyrid
meteor with beginning height above 130 km.
Surprisingly, the eta-Aquarids and the Lyrid were
not bright enough to be recorded by all-sky
photographic cameras. PSA-10
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Light Curves of Faint Meteors
Pavel Koten and Jiri Borovicka (Astronomical
Institute, Academy of Science, Ondrejov
Observatory, 251 65 Ondrejov, Czech Republic)
The results of the analysis of light curves of
about 250 meteors observed and recorded within the
double-station image intensifier observations at
the Ondrejov observatory will be presented.
Double-station observations allow to compute the
meteor trajectory in the Solar system and in the
atmosphere as well as to determinate the absolute
magnitude of meteor and its mass. Light curves and
heights data of all major meteor showers &emdash;
Lyrids, eta-Aquarids, Perseid, Orionids, Leonids,
Geminids as well as many sporadic meteors &emdash;
were analysed. The differencies between individual
showers were found, e.g. Perseids appear to be more
compact than Leonids. There is also difference
between 1998 and 1999 Leonids. This suggests
different composition or structure of parent
bodies. Our data show that the beginning heights of
Perseids, Orionids and Leonids are weakly dependent
on meteor mass, although the dust-ball theory
assumes they should be mass independent. 3.5
Some Features of Digital Kinematic and
Photometrical Processing of Faint TV Meteors
Pavlo M. Kozak, Alexander A. Rozhilo and Yury G.
Taranukha (Astronomical Observatory of Kyiv Taras
Shevchenko National University, Kyiv, Ukraine
Some features of digital kinematic and
photometrical processing of TV faint meteors are
discussed. For these purpose a computer original
program has been worked out. The program uses data,
obtained by two TV devices, equipped by izokon TV
tubes. Observational images were recorded into
videotaperecorder and than digitized with the help
of a framegrabber. A precision of measurements of
meteor coordinates in the frame is estimated.
The kinematic processing is based on an original
method using in general elements of vector analysis
and calculates both meteor trajectory parameters in
Earth's atmosphere and orbit elements. The errors
of the parameters are also computed. Photometrical
characteristics of TV systems were investigated.
Some experiments for photometrical field
correction, spectral sensitivity of TV tube cathode
and correction for the motion of a meteor were
carried out. The method was approbated on the
results of basic observations of meteors for the
last years in Kyiv. PSA-31
Thermal Explosions of Meteoroids in the Earth's
Atmosphere
V.G. Kruchynenko (Astronomical Observatory of
Taras Shevchenko Kiev University, Ukraine)
Based on a data analysis about bright flashes of
large meteoroids in a terrestrial atmosphere
(Tungusskiy, Sichote &emdash; Alin, Sterlitamak,
Kun'-Urgench etc.) we come to a conclusion, that
such thermal explosions happen at the height of
maximum deceleration. Such assumption confirms also
explosion of Shoemaker-Levy 9 comet in atmosphere
of Jove. In this area on a small interval of
altitudes (significant less than altitude of a
homogeneous atmosphere, therefore explosion can be
considered as the point one) the loss of energy by
a body on deceleration surpasses energy, which is
indispensable for a full evaporation of whole body.
At the same time, achievement by a meteoroid of the
altitude of maximum deceleration is condition
indispensable, but not sufficient that there was a
thermal explosion. It is known the meteoroids,
which reach the altitude of maximum deceleration,
but explosion does not happen. For the analysis of
conditions in the field of maximum deceleration the
indispensable mathematical model is developed. We
also suppose, that at collision of bodies with any
environment (water, rock, metal) the explosion of
the impacting projectile happens (more correctly:
is possible) only on a depth of its maximum
deceleration in given environment. 5.3
The Modal of the Quasi-continuous Fragmentation
and its Application to the Analysis of Meteoric
Observations
V.L. Kuznetsov and G.G. Novikov (Novgorod State
University, Novgorod the Great, Russia)
The amount of data evidencing fragmentation led
Levin (1963) to the conclusion that, if
fragmentation were not taken into consideration in
processing the observations, erroneous results
would results. Knowledge of sizes and masses of
particles, which separate from a meteor body or on
which it is fragmented during moving in atmosphere
of the Earth, is of interest for understanding of
processes of its interaction with air, and for
improvement of our notion idea of a structure of
meteor bodies. The new formula, describing an
appearance of fragmentation is obtained on the
basis of a new mathematical model approach to
solution of the task about fragmentation of a
meteoric body the quasi-continuous type. The new
approach has allowed describing two kind
quasi-continuous fragmentation (QCF) of uniform
mathematical formula. The limiting case slow QCF is
the pure evaporation and the limiting case fast QCF
is the flares of meteors in its classical
definition are exhibited. The method of the
analysis of meteoric observations, introduced in
the catalogues containing information about height
of maximum of a brightness and values of a
brightness at these heights to definition by the
parameters QCF are represented. 3.4
Contemporary Interstellar Meteoroids in the
Solar System: In-situ Measurements and Clues on
Composition
M. Landgraf (ESA/ESOC, 64293 Darmstadt,
Germany)
Meteoroids originating from the local
interstellar medium traverse the solar system. This
has been proven by in-situ measurements by
interplanetary spacecraft as well as by highly
sensitive radar measurements. Early attempts to
detect interstellar meteoroids using the
instruments on board the Pioneer 8 and 9 spacecraft
failed. More sensitive detectors on board the joint
ESA/NASA mission Ulysses as well as on board the
NASA spacecraft Galileo, however, unambiguously
detected meteoroids of interstellar origin. This
discovery has started efforts to compare the
results from the in-situ measurements with highly
sophisticated models of interstellar dust
properties derived from astronomical absorption and
extinction measurements. It was found that, at
least locally, is more mass locked up in meteoroids
than expected from the astronomical measurements.
So far the in situ measurements only allow to
derive composition information indirectly via the
meteoroid's dynamics. 11.1
Clues to the Structure of Micrometeoroids, from
Dust Light Scattering Properties
A.Ch. Levasseur-Regourd, E. Hadamcik and V.
Haudebourg (Université Paris VI and Service
d'Aeronomie, CNRS-IPSL)
Knowing the size distribution and the shape
(compact or fluffy) of the dust particles in meteor
streams is of major importance, to understand their
mechanisms of interaction with the atmosphere and
their impacts effects on spacecraft. Some clues are
provided through observations of the solar light
scattered by cometary and interplanetary dust
particles. While their brightness and polarisation
phase curves are mostly similar, and indeed
characteristic of irregular particles, major
differences are noticed (both from remote and
in-situ observations) in terms of polarisation
levels and polarisation colours. These differences
correspond to different formation regions, and also
reveal an evolution of the dust morphological
properties, linked to fragmentation and evaporation
processes. Recent results from computational models
and laboratory measurements will be presented,
including polarisation phase curves of samples of
terrestrial or meteoritic origin, and results of
the CODAG experiment, launched from Esrange in May
1999. 10.6
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The IAU Meteor Data Center
B.A. Lindblad (Lund Observatory, Lund,
Sweden)
The IAU Meteor Data Center (MDC) in Lund acts as
a central depository for meteor orbits obtained by
photographic, video and radar techniques. It was
started in 1978 at the suggestion of the present
author. The photographic data sample now consists
of 4580 precisely reduced orbits plus 2401
graphically reduced orbits. The reformatting of the
precisely reduced orbits to a standard format has
been a major undertaking since each author/station
has used a somewhat different format. There is also
some overlap between the various catalogues. For
details see the IAUMDC Documentation pamphlet.
As of 1 January 2002 the responsibility of
operating the MDC will be transferred to the
Astronomical Institute of the Slovak Academy of
Sciences in Bratislava, Slovakia with Dr. V.
Porubcan as the responsible scientist.
Dr. V. Porubcan and co-workers have been
involved in various studies of the photographic
data-base. They are preparing a new version which
is based on the year 2000 equinox (instead of the
1950 equinox used in nearly all of the published
catalogues). They have also made extensive studies
of the errors in some of the older photographic
data. A description of this work is presented in
Lindblad, Neslusan, Svoren and Porubcan (2001).
PSA-1
Visual and Radar Observations of the Perseid
Meteor Stream 1953-83
B.A. Lindblad (Lund Observatory, Box 43, SE-221
00 Lund, Sweden)
This paper describes a long term,
high-resolution study of the activity of the
Perseid meteor stream based on visual and radar
observations at the Onsala Space Observatory in
Sweden. The data sample consists of 147 visual
hourly rates and some 2000 radar hourly rates
recorded in mid-August in the period 1953-83. In a
previous paper (Lindblad 2000) a high-resolution
study of the visual zenithal hourly rates of bright
Perseid meteors versus solar longitude was
described. The study using a step length of
0.05° in solar longitude, revealed that the
Perseid activity curve has a multi-peak structure
with at least four separate and well-defined peaks
in the activity curve of bright Perseid meteors. In
the present paper we analyse more than 2000 radar
hourly rates obtained during the same period. Each
hourly rate is available in three different echo
duration classes. It is well known that the
percentage of Perseid meteors is highest amongst
the echoes of long duration. We therefore here
analyse hourly rate counts of echoes of duration
1.0 sec and longer, corresponding approximately to
visual magnitudes of 2.5m and brighter. The
activity curve of the Perseid stream based on these
bright meteors is studied. The radar data very
strongly support the previous visual data
indicating several separate and permanent peaks of
stream activity. 1.1
Cosmic Dust and Micro-debris Measurements on
Space Station MIR
J.C. Mandeville and M. Bariteau (ONERA/DESP, 2
Av. E. Belin, 31400 Toulouse, France. e-mail:
jean-claude.mandeville@onecert.fr)
Investigation of impact features found on
material retrieved from low earth orbit, after
exposure to space for a long period of time, has
provided us with a great deal of data on the
particulate environment, either natural or
man-made. Between 1987 and 1997, several detection
devices have been deployed outside the Russian MIR
space station. The passive sensors are composed
primarily of stacked thin metal foils (gold and
aluminum). The size of holes or impact craters give
information on the size or shape of the impacting
particles. In addition, solar cells from a solar
array retrieved by a Shuttle-MIR mission have been
searched for impact craters. Samples have been
retrieved for laboratory analysis and flux of
impacting particles has been derived. Comparison
with data from LDEF, and HST provides insight in
the long-term evolution of small particle
population and in the debris environment of a
permanently manned station. Between 1987 and 1997,
no peculiar enhancement in the population of
microdebris in the vicinity of the MIR station was
seen. Several samples show evidence of secondary
impact cratering: an attempt is made to locate the
origin of primary impact sites. For routine
monitoring of space environment the method provides
a low cost and reliable tool, if the retrieval of
material is possible. However, as short-term
fluctuations in the flux of particles are not
visible with passive experiments, they should
benefit from data obtained by active experiments.
9.2
Cosmic Dust near 1 AU
Ingrid Mann (1, 2), Håkan Svedhem (1), Sho
Sasaki (3), Eduard Igenbergs (4), Gerd Hofschuster
(4), Walter Naumann (4), and Hideo Ohashi (5)
1) ESA Space Science Department, ESTEC,
Noordwijk, The Netherlands; 2) Institute of
Planetology, The University of Muenster, Germany;
3) The University of Tokyo, Japan; 4) Fachgebiet
Raumfahrttechnik, TU Munich, Germany; 5) Tokyo
University of Fisheries, Japan
Cosmic dust near 1 AU results from the collision
evolution of dust produced from comets, asteroids
and meteoroids. Moreover, dust particles entering
the solar system from interstellar space are
detected near the Earth orbit. Knowledge of the
size distribution and of the orbital distribution
of dust near 1 AU therefore helps to understand the
sources of the dust cloud as well as its collision
evolution. We discuss the velocity distribution of
dust near 1 AU as well as the collision evolution
of dust and the production of beta-meteoroids that
leave the solar system in hyperbolic orbits.
Moreover we discuss the expected flux of
interstellar dust and its gravitational focussing.
We finally refer to dust measurements of the Mars
Dust Counter experiment onboard the Japanese
mission Nozomi that works since 1998. Nozomi
measurements near Earth have detected particles
with masses 10-17 kg < m < 10-12 kg. The
Nozomi measurement planned during the next phase of
the mission will provide dust fluxes between about
1 and 1.6 AU. PSB-20
Dust and Meteoroids in Extra-solar Planetary
Systems
Ingrid Mann (1, 2) and Malcolm Fridlund (1)
1) ESA Space Science Department, ESTEC,
Noordwijk, The Netherlands; 2)Institute of
Planetology, University of Münster,
Münster, Germany
Basic properties of the evolution of the solar
system meteoritic complex are also expected to be
important for the evolution of circum-stellar
debris disks: Mutual Collisions and Poynting
Robertson effect limit the lifetime of dust
particles in Keplerian orbits around stars if the
density of circum-stellar gas is sufficiently
small. While "dense" dust shells such as the shell
around Beta-Pic are limited by collision lifetime,
mutual collisions get less important for systems
with lower dust density. The evolution of dust and
meteoroids from their sources can cause, similar to
meteor streams, local features in circum-stellar
dust shells. We discuss the compatibility of solar
system and "extra-solar" conditions for the
evolution of planetesimals, meteoroids and dust
particles. 11.3
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Meteor Trains as a Probe for Measuring the
Dynamics of the Upper Atmosphere
Steven Marsh and Jack Baggaley (University of
Canterbury, Christchurch, New Zealand)
The AMOR meteor orbit radar operated in New
Zealand has recently been extended to enable wind
measurements in the upper mesosphere/lower
thermosphere. As a meteoroid encounters the
increasing density of the Earth's atmosphere it
ablates and leaves a train of ionisation. Radar
signals reflected from this atmospherically
transported train are Doppler shifted and a line of
sight wind measurement can be made. Aside from
information about atmospheric dynamics, a correct
interpretation of meteoric signatures requires an
understanding of the influence of such motions. A
dual interferometer enables the wind measurement's
height to be determined to within 1 km. Hence a
detailed vertical profile of atmospheric motion in
the meteor region is obtained. This paper details
the meteor radar method of wind measurement.
Results presented include a time series analysis of
the AMOR winds data. This reveals a strong 12-hr
semidiurnal tide as well as occasional planetary
wave activity. Evidence suggesting the presence of
gravity waves, possibly produced from the local
Southern Alps mountain range, breaking in the
meteor region will also be given. PSA-36
The Role of Large-Aperture V/UHF Radar Meteor
Observations in Meteor Science
J. D. Mathews (1), D. Janches (2,1), D. D.
Meisel (3,1), Q.-H. Zhou (4), S. Close (5) and A.
Pellinen-Wannberg (2)
1) Communications and Space Sciences Laboratory,
The Pennsylvania State University, University Park,
PA 16802-2707 USA; 2) Swedish Institute of Space
Physics, Box 812, S-981-28, Kiruna Sweden; 3) Dept.
of Physics & Astronomy, SUNY-Geneseo, Geneseo,
New York, 14454-1401 USA; 4) Arecibo Observatory,
Box 995, Arecibo, Puerto Rico 00613; 5) MIT Lincoln
Laboratory, Lexington, MA 02420-9108 USA
Meteor science based solely on "classical"
HF/VHF meteor radar observations was characterized
by a number of long-standing unresolved issues that
have been solved or refined with the advent of
radar meteor observations made using high-power,
large-aperture V/UHF radars. These radars include
those located at Arecibo Observatory, the Jicamarca
Radio Observatory, EISCAT, and the MU and ALTAIR
radars. Radio science issues successfully addressed
with the new observations include the origins of
"head-echoes" and anomalous trail-echos. Meteor
trails have been found to rapidly B-field align
throughout the 80-120 km altitude meteor-zone
giving rise to FAI (field-aligned irregularity)
scattering. Doppler observations have resolved
issues related to the speed-distribution of at
least micrometeoroids and micrometeoroid mass
fluxes have been found. Additionally, it is
becoming clear that assumptions regarding
ionization mechanisms for the smallest meteoroids
must be reexamined. Finally, we note the planetary
astronomy role of these radars in providing vast
numbers of micrometeoroid instantaneous orbits.
7.2
Updated Micrometeoroid Mass Flux Results from
Arecibo Meteor Observations
J. D. Mathews (1), D. Janches (2,1), D. D.
Meisel (3,1) and Q.-H. Zhou (4)
1) Communications and Space Sciences Laboratory,
The Pennsylvania State University, University Park,
PA 16802-2707 USA; 2) Swedish Institute of Space
Physics, Box 812, S-981-28, Kiruna Sweden; 3) Dept.
of Physics & Astronomy, SUNY-Geneseo, Geneseo,
New York, 14454-1401 USA; 4) Arecibo Observatory,
Box 995, Arecibo, Puerto Rico 00613
Radar micrometeor observations at Arecibo
Observatory enable direct estimates of the
meteoroid mass flux into the upper atmosphere. We
report updated mass flux determinations from
November 1997/1998 observations that are based on
the observed number of meteor events per day in the
300-m diameter Arecibo beam and on particle mass
determinations from that fraction of all particles
for which deceleration is measured. The average
mass of the Arecibo micrometeoroids that manifest
observable deceleration is ~0.5 microgram/particle
with a resultant annual whole-Earth mass flux of
~2.2¥106 kg/yr over the 10-5-102 microgram
mass range. The annual whole-earth mass flux per
decade of particle mass is calculated and compared
with that of Ceplecha et al. [1998]
(3.7¥106 kg/yr) and with that derived by Love
and Brownlee [1993] (LB) from small
particle impact craters on the orbital Long
Duration Exposure Facility (LDEF). We also give the
LDEF results as significantly modified using the
Arecibo-determined average particle velocity of 50
km/sec-much larger than the effective value of 12
km/sec used by LB. This modification results in a
net LDEF mass flux of 1.8¥106 kg/yr-about 7%
of their original result. These results may
continue to provoke debate. PSA-32
The AKM Video Meteor Network
Sirko Molau (International Meteor
Organization)
The German Arbeitskreis Meteore (AKM) group has
been installing and operating a network of
automated image-intensified video cameras since
March 1999. It is based on the MetRec meteor
detection and analysis software, which allows for
efficient video observations with only a minimum of
human interaction. It is the first network of video
cameras ever that operates on a regular basis and
collects large amounts of meteor data in the
optical domain throughout the full year. As of
spring 2001, the network consists of ten stations.
Further stations in Germany and abroad are
preparing to join the effort, expanding the AKM
network into a global one. All data are compiled
into an archive that is freely accessible through
the Internet. The video meteor database contains
currently more than 24.000 single-station meteor
records from about 400 observing nights. The talk
will describe the development and current status of
the MetRec software including a short
demonstration. An overview over the present state
of the network will be given. We will describe the
structure of the database and illustrate its
application. Future plans like the automatic
analysis of multi-station video observations and
thorough meteor shower analyses will be addressed
in the outlook. 4.3
Constraining Cometary Ejection Models from
Meteor Storm Observations
Michael Mueller, Simon F. Green and Neil McBride
(Planetary and Space Science Research Institute,
Open University, Walton Hall, Milton Keynes, MK7
6AA, UK)
Modelling and observations of the Leonid
activity in recent years have shown that maxima in
the meteor storm activity can be identified to be
due to particles released from the comet during a
certain perihelion passage. If the particles
originating from a certain perihelion passage can
be identified, it is an obvious next question to
ask what information can be gained about the
ejection process of particles from a cometary
nucleus. To address this question we have developed
a model which allows calculation of the particle
number density in a dust trail physically
consistent for arbitrary complex activity
distributions of a comet with numerical integration
of only relatively few trajectories. The model is
applied to the Leonid activity in the year 2000. It
is shown that particles of different sizes entering
the Earth atmosphere at the same time were released
from the comet at different heliocentric distances.
Therefore one has to make assumptions about the
activity of the comet with heliocentric distance in
order to derive the cometary size distribution from
an observed meteor size distribution. However, it
is shown that lower limits on the ejection velocity
of the observed particles can readily be derived.
1.8
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Physics and Chemistry of Meteoroids in the Upper
Atmosphere
Edmond Murad (Space Vehicles Directorate, Air
Force Research Laboratory, Hanscom AFB, MA 01731,
USA)
Meteoroids entering the Earth's atmosphere are
frictionally heated by collision with atmospheric
gases and begin to ablate at altitudes ranging from
130 to 100 km, depending on their initial
velocities, sizes, and densities. An important
question in this entry is whether the thermal
properties of the meteoroids can reach equilibrium
within the transit time of the meteoroids from the
point of entry to the point where they are slowed
down. If equilibration can occur quickly enough,
then evaporation would follow the laws of
equilibrium thermodynamics. If not, then
time-dependant thermodynamics have to be invoked.
Arguments for the former and their implications
will be presented during this talk. 3.1
Meteor Head Echo Observations by the MU Radar
and Simultaneous ICCD Camera Observations
Takuji Nakamura (Radio Science Center for Space
and Atmosphere, Kyoto University) Toru Sato and
Koji Nishimura (Graduate School of Informatics,
Kyoto University)
The MU radar (middle and upper atmospheric
radar) is a VHF Doppler radar with a high output
power (46.5MHz, 1MW) with a large circular array
antenna (8330m2). This radar has been used for both
atmospheric and meteoric studies by receiving
meteor tail echoes for over a decade. Recently, we
have applied the MU radar for measurement of meteor
head echoes and further developed two different
techniques for instantaneous measurement of meteor
orbits: the sequential beam lobing method and the
intereferometric method. The latter is found to be
more precise in orbit determination because of
rapid variation of radar cross section of head
echoes. Precision of this method is estimated to be
0.2 km/s and 0.5 degree for meteor speed and
velocity vector direction, respectively.
Simultaneous optical observation with an ICCD
(image intensified CCD) camera system (sensitive to
+9 mag. meteors) was carried out. From 229 minutes
observation, 1393 meteors were detected with the
radar and 34 meteors were simultaneously recorded
by the optical system. Comparative analysis
revealed that our radar observation is capable of
determining orbit of faint meteors up to +14.8
magnitude. Meteor velocity distribution and mass
estimation will also be reported in the paper.
4.5
Observation of Leonid Activity in 1998 and 1999
with the MU Radar and an All-sky TV Camera
Takuji Nakamura, Sigeru Asakura and Toshitaka
Tsuda (Radio Atmospheric Science Center, Kyoto
University), Masayoshi Ueda (Nippon Meteor Society)
and Jun-ichi Watanabe (National Astronomy
Observatory)
The MU (middle and upper atmosphere) radar
observed a significant Leonid activity both in 1998
and 1999. A very strong activity with strong and
long lasting meteor echoes was observed between 21
UT on Nov. 16 and 02 UT on Nov. 17 (06-11 LT) in
1998. On the other hand, in 1999, a severe outburst
with strong but much shorter echoes was detected
just around the expected peak time of 2 UT on Nov.
18, 1999 (11 LT). In order to estimate the visual
magnitude and mass of the meteors during such
shower activity, we carried out an all-sky TV
observation with an image intensifier
simultaneously. By applying the ionized tail model
with attachment process of electrons, radar echo
durations are converted to meteor magnitudes. As a
result, we conclude that there were plenty of and
few fireballs (e.g., brighter meteors with
magnitude of -3 ) in 1998 and 1999. We further
discuss about the total mass of meteors during the
two outburst cases. PSA-29
Comparison among the Keplerian-orbit-diversity
Criteria in Major-meteor-shower Separation
L. Neslusan and P.G. Welch
Recently, two new criteria of diversity of
Keplerian orbits have been suggested, that by
Valsecchi, Jopek, and Froeschle (VJF) in 1999, and
orbital-momentum-based (OMB) criterion by Neslusan
in 2001. In the presented paper, there is a
comparison of how the classic, Southworth-Hawkins
(SH) criterion from 1963, and both new criteria
behave, when these are used in the separation of
several major meteor showers from the photographic
IAU MDC database. The
cumulative-number-on-threshold-D-dependence method,
based on work by Sekanina from the beginning of
seventies, is utilized to perform an optimal
separation. The quality of separation is evaluated
with the help of "background-number-density test"
(described here in more detail). No general
difference among the particular criteria was found.
A relatively worse result is obtained using SH
criterion for Perseids. The separation method does
not work with the VJF and OMB criteria for the
alpha-Capricornids, and with OMB criterion for the
Northern as well as Southern delta-Aquarids.
PSA-9
Lifetimes of Meteoroids in Interplanetary Space:
The Effect of Erosive and Catastrophic
Collisions
S. Nikolova, J. Jones (Department of Physics and
Astronomy, University of Western Ontario, London,
Ontario, N6A 3K7 Canada)
There are a number of mechanisms that affect the
lifetimes of meteoritic material in interplanetary
space. These include Poynting-Robertson effect,
Radiation Pressure, Electromagnetic forces and
collisions with other meteoritic particles. A
physical model of the sporadic meteoroid complex
was recently developed by Jones, Campbell and
Nikolova. The model considers short and long period
comets as primary sources of meteoritic material
and Poynting-Roberston effect as dominant mechanism
of orbital change. This paper investigates the
lifetimes of meteoroids against erosive and
catastrophic collisions including the effect of
orbital inclination using spatial density
distributions obtained by the latter model.
10.5
About Pulsation Brightness of the Bright
Meteors
G. G. Novikov and O.V. Sokolov
On the example of the solution of the model
problem it is shown that one of the possoble
reasons of pulsation of the brightness of the
bright meteors is rotation. Theoretically counted
curves of the brightness for the meteoroids, having
the cubic and sellipsoid forms qualitatively agree
with the observations. PSA-27
The Global Monitor of Meteor Streams by Radio
Meteor Observation
Hiroshi Ogawa, Shinji Toyomasu, Kimio Maegawa
and Koji Ohnishi
In recent years, in Japan, Radio Meteor
Observation(RMO) has spreads, and RMO has come to
be observed by many observers. Then, to grasp the
whole aspect of meteor stream activity accurately,
the necessity of unifying the observational data
all over the world came out. Then, we tried to
correct and integrate them. To consider the error
by geographical factor or the observational
equipment, the data was divided by average counts
previous one week. The 2000 Leonids RMO result at
eight sites of the world was unified by this
method, and three peaks appeared. This is similar
to the result of Visual Observation. In this time,
however, it was considered without using the radar
equation etc, we could get result as almost same as
Visual Observation. Therefore, the more exact
result could be obtained if we consider of it.
However, it cannot unify easily now, because we
have poor information on the various equipment and
various geographical conditions. It cannot unify
easily at a present stage. Consequently I would
like to collect the detailed data of each
observational site, and to establish the method of
catching meteor stream activity accurately.
PSA-17
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A New Meteor Shower, eta Eridanids
Katsuhito Ohtsuka (Tokyo Meteor Network) and
Tomoyasu Tanigawa (Nishinomiya-Nishi High
School)
From among approximately 1000 optical meteor
data obtained during the past few decades, we
discovered a total of 5 (4 probable and 1 possible)
meteors which belong to a new meteor shower, eta
Eridanids. Several visual and radar observations
reinforces the evidence that the eta Eridanids
surely exist. We also found out Comet D/1827M1
(Pons-Gambart) and Comet C/1852K1 (Chacornac) as
the parent comet candidates. However, the eta
Eridanids are rather associated with Comet
Chacornac than Comet Pons-Gambart, judging from
their orbital similarities. PSA-8
On Electrophonic Phenomena
A.Yu. Ol'khovatov (Radio Instrument Industry
Research Institute, Moscow, Russia)
During last years an idea that electrophonic
sounds are caused by VLF electromagnetic radiation
from a bolide's wake is promoted again. The source
of the radiation is considered to be "magnetic
spagetti relaxation" in a bolide's wake. The most
serious problem with the theory is that level of
detected VLF disturbances, accompanied a bolide is
negligibly small, comparing with needed for hearing
VLF radiation. For example, C. Keay experiments
revealed lower limit of hearing in order of 160
V/m. It means that a bolide producing electrophonic
sounds is to generate in its wake VLF radiation
with the power at least in order of 1012 W. Nor
present theory neither experiments with turbulent
ionized wakes predicts such superpowerful VLF
radiation. Anyway, if it is realized somehow, it
would lead to spectacular effects, for example, to
enormous Joule heating of the wake (due to
extremely large electric currents) transforming the
wake into object as bright (seen from the ground)
as at least the Sun. And, of course, this
"super-radiation" would produce remarkable global
effects &emdash; but none of them are known. The
presence of "transducers" near an observer can't
help the situation, as the needed level to hear
their vibrations are even in order of magnitude
larger, and anyway, it can't be lowered down many
orders of magnitude. A solid confirmation that
these estimations are correct is the fact that
otherwise people would hear numerours VLF
transmitters hundreds miles away! Also there were
reports of electrophonic sounds during several
Space Shuttle re-entries. The the hypothetical
"super-radiation" (if exists) would produce a very
remarkable (devastating) effect on the spaceplane.
Also, in many electrophonic events the power of
aerobraking, i.e. the power deposited by a
meteoroid into the atmosphere, which is to be the
energy source of the proposed VLF super-radiation
was much less that the power of the latter. 8.5
A Problem of a Meteor Head Echo
A.Yu. Ol'khovatov (Radio Instrument Industry
Research Institute, Moscow, Russia)
An unresolved problem of meteor physics is the
meteor head echo, i.e. a radar target moving with a
meteor velocity. About a decade ago the author has
proposed that a head echo is caused by generation
of plasma waves in surrounding ionospheric plasma
and in meteor's ablation products. The ion beam
instability could be a one of sources of the plasma
waves, as at the head echo heights a density of
ions "sprayed and repelled" by a meteoroid is
rather high, and moreover, the ions are weakly
trapped by geomagnetic field. Probably these
processes at high altitudes were videotaped during
the 1998 Leonids campaign. Also maybe coupling with
some types of ionospheric waves is important also.
This interpretation of a head echo predicts some
shift between a meteoroid velocity calculated from
its trajectory, and from its Doppler radar return,
due to the plasma waves. And it seems that the
prediction are being confirmed. Recent radar data
indicate some difference between these two
velocities. PSB-8
Non-specular Meteor Trails: What Does Linear
Plasma Theory Teach us about Field-aligned
Irregularities?
Meers Oppenheim, Lars Dyrud, Sigrid Close and
Stephen Hunt (Center for Space Physics, Boston
University)
Radars probing the atmosphere between 75 and 120
km frequently receive echoes from plasma trails
left by ablating micron-sized meteors. These echoes
have proven useful in characterizing the meteors
and in estimating high altitude wind velocities and
temperatures. Measurements of non-specular radar
echoes and recent plasma simulations demonstrate
that field-aligned irregularities develop within
meteor trails. This paper analyzes the plasma
physics of meteor trail irregularities and compares
the results with simulations and observational
data. This study helps us better understand the
composition of meteor trails and their interactions
with the surrounding atmosphere. In particular, we
can evaluate: (1) criterion for the onset of the
instability as a function of altitude, meteor trail
composition and density, and temperature; (2) the
nature of the instability and the resulting waves;
(3) the range of unstable wavelengths both
perpendicular and oblique to the geomagnetic field;
and (4) the growth rates at each wavelength. This
analysis should enable us to better use meteor
radar data to characterize meteors and the upper
atmosphere. 5.5
On the Variable Meteors Parameters
Petr Pecina (Astronomical Institute, Academy of
Sciences, Ondrejov Observatory 251 65 Ondrejov,
Czech Republic)
The problem of variable shape-density
coefficient and ablation parameter is discussed.
The two new alternatives to the approaches
published so far are proposed. Both alternatives
are based on the observed distances flown by a
meteoroid considered as a function of time and on
the observed light curve again as a function of
time. The first alternative deals with the case of
isotropic ablation of a body while the second one
considers its cross-sectional area to be a general
function of time. As a result, the time dependence
of both parameters as inferred from the
observational data of 5 fireballs, is shown. As a
byproduct, there is also presented the exponent in
the light efficiency dependence, tau, on velocity
(in the power form), for each fireball. 3.7
Relation between the Optical and Radar
Characteristics of Meteors
Petr Pecina, Pavel Koten, Rosta Stork (Petr
Pridal Astronomical Institute, Academy of Sciences,
Ondrejov Observatory 251 65 Ondrejov, Czech
Republic)
Some results on simultaneous TV double station
and radar observations of meteors performed in the
Czech Republic in 1998 and 1999 are presented. The
relation of the magnitude of each TV meteor, in the
height corresponding to the radar reflection point,
to the radar amplitude or the duration of the echo,
is studied. 6.4
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TV and Radar Observation of Meteors
Petr Pecina, Pavel Koten and Rosta Stork (Petr
Pridal Astronomical Institute, Academy of Sciences,
Ondrejov Observatory, 251 65 Ondrejov, Czech
Republic)
The identification of simultaneously observed TV
and radar meteors is usually based on time
coincidence of both events. The derivation of the
range the TV data yields for the radar one in case
when the radar station does not coincide with any
TV station, is presented. Since also the height of
meteor is important quantity we performed the
derivation of formulae providing us with the height
of the radar reflection point in case when only one
TV station observation accompanied by the radar one
was made. PSB-4
The High Power Large Aperture Radar Method for
Meteor Observations
Asta Pellinen-Wannberg (Swedish Institute of
Space Physics, Box 812, SE-981 28 Kiruna,
Sweden)
The high power large aperture radar meteor
method will be presented. It is compared to the
classical meteor radar method in terms of working
frequency ranges, beam widths, power and radar
energy fluxes at meteor altitudes to show their
crucial differences. The classical meteor radars
are sensitive to perpendicular meteor trails and
are thus perfectly suited for shower meteor
observations when orienting the radar beam
perpendicular to the radiant direction. By
contrast, the large aperture radars, due to their
working frequencies and high power, observe the
meteoroid-atmosphere interaction at all
look-angles. Tristatic measurements from the EISCAT
UHF system show that the scattering is isotropic up
to angles of 110°. Due to the high sensitivity
and narrow beams of these radars they mainly
observe the numerous populations of the very small
sporadic background particles. Hardly any
shower-related increase in fluxes has been observed
in the EISCAT Geminid, Perseid and Leonid
observations and in the Arecibo Leonid
observations. Simultaneously with meteor modes the
radars can operate in their usual incoherent
scatter modes to observe the electron density
variations in the background ionosphere. Thus
evolution of sporadic E layers, their average ion
composition and their relation to meteor activity
can be monitored. 7.1
The Impact of Extra-terrestrial Dust on the
Upper Atmosphere
John Plane (School of Environmental Sciences,
University of East Anglia, Norwich, U.K.)
More than 100 tonnes of inter-planetary dust
enters the earth's atmosphere each day. Most of
this material ablates in the upper esosphere and
lower thermosphere, giving rise to a rich diversity
of phenomena. For instance, thin layers of metal
atoms such as Na, K, Fe and K occur globally at an
altitude of about 90 km. These can be observed from
the ground by lidar, providing very detailed
information about the physics and chemistry of this
little explored atmospheric region. Metallic ions
in the E region are largely responsible for the
formation of sporadic E layers, which have an
important effect on communications and the global
electricity circuit. Meteoric debris also slowly
recondenses to form dust particles, which may act
as condensation nuclei for noctilucent clouds and
polar stratospheric clouds which activate the
chlorine-catalysed removal of ozone. Metallic dust
may also provide catalytic surfaces for reactions
such as O + H2 to form water.
This paper will focus on a number of recent
laboratory and modelling studies by the group at
Norwich. The experimental work will include: the
reactions of FeO, MgO and CaO with atmospheric
constituents such as O3, O2, CO2 and H2O; the
reactions of atomic O with FeO, FeO2 and FeO3; the
reaction between NaHCO3 and H, demonstrating
closure of the atmospheric Na cycle; and the
photochemistry of sodium species such as NaOH and
NaHCO-3. The modelling and theoretical work will
include: a rigorous test of the proposed
ion-molecule mechanism for the formation of
sporadic Na layers; a model of metallic species
acting as ice particle nuclei; and a new diurnal
model of the Na layer which provides prima facie
evidence for the removal of Na-containing molecules
through dust formation. 5.1
Formation of Disturbed Area around Fast Meteor
Body
O.P. Popova, S.N. Sidneva, A.S. Strelkov and
V.V. Shuvalov (Institute for Dynamic of Geospheres,
Russian Academy of Sciences)
The ablation of meteoroids essentially
influences on all processes connected with or
initiated by meteoroid entry. Evaporated meteor
substance interacts with incoming air flow and
forms disturbed area both around and behind the
meteor body. There is no yet complete theory of a
single high altitude meteor, which could allow to
estimate thermodynamical parameters and radiation
of formed area by self-consistent way.
Air-meteoroid interaction may be described in the
frame of particle-beam model which permits to
estimate parameters of formed vapor. It includes
both gasdynamical and statistical simulations. The
solution of Boltzman equation by the Monte Carlo
method allows to consider air particles
interactions with meteor body and vapor cloud
formed around it. The influence of non-elastic
processes is estimated and discussed. This
technique permits to determine the energy, momentum
and mass transfer and consider not only primary
particle interaction but also the fate of secondary
formed particles. The gasdynamical description is
used for vapor cloud formed as the result of
ablation, nearby wake evolution, radiation field.
3.2
Five-year Cooperative Radio Observations of the
Leonid Meteoroid Stream by the BLM Radar System
V.Porubcan (1), A.Hajduk (1), G. Cevolani (2)
and G. Pupillo (2).
(1) Astronomical Institute, Slovak Academy of
Sciences, 84228 Bratislava, Slovakia, (2) Istituto
ISAO-CNR, via Gobetti 101, 40129 Bologna,
Italia
A survey of results from joint campaigns of the
Leonid meteoroid stream observed by the BLM
(Bologna-Lecce-Modra) forward scatter system in
1996-2000 is presented. The Leonid radio
observations were carried out on November 10-20
each year along two baselines: Bologna-Lecce
(Italy) and Bologna-Modra (Slovakia). Trends of
long duration echoes and variations of reflection
time exhibit a multiple peak activity which is
possibly connected with a filamentary structure of
the Leonid meteoroid stream. The mass distribution
exponents of the Leonid meteoroids in the period of
the shower peak activity show significant changes
throughout the 5-year observational period, with a
higher representation of larger particles mainly in
1998 and 2000, and of relatively smaller particles
during the minor meteor storm in 1999. The multiple
peak activity and variations of mass exponent in
the observed period resulting from forward scatter
observations are consistent with the results
obtained by other techniques. 2.6
[To top of page]
The Updated Version of the IAU MDC Database of
Photographic Meteor Orbits
B. Lindblad (1), L. Neslusan (2), J. Svoren (2)
and V. Porubcan (3)
(1) Lund Observatory, 22100 Lund, Sweden, (2)
Astronomical Institute, Slovak Academy of Sciences,
05960 Tatranska Lomnica, Slovakia, (3) Astronomical
Institute, Slovak Academy of Sciences, 84228
Bratislava, Slovakia
The database of photographic meteor orbits of
the IAU Meteor Data Center in Lund has gradually
been updated. The version 2001, which has been
prepared for publication and which will be released
soon, contains complete orbital and geophysical
data on 4581 meteors. Several catalogues have been
published in some stations and thus a given
publication serial number may correspond to several
meteors. To remove ambiguity, we now introduce a
new meteor identification code consisting of the
publication serial number, the author or station
code, and the number of the catalogue. The database
contains geophysical parameters and orbital
elements, which are mutually dependent. Therefore
one set can be used to verify the correctness of
the other. This verification and appropriate
corrections are done. The distribution of database
is again planned as two separate files: one with
orbital, another with geophysical data. A file
containing all data merged and orbits homogenized
will be available, too. All the files as well as
the appropriate documentation will be placed on a
WWW-site to enable their free, public downloading.
PSA-12
On Periodic Activity Variations during the 1999
Leonid Meteor Storm in Various Data Sets
Jurgen Rendtel (International Meteor
Organization, Potsdam, Germany).
Observational data obtained during the 1999
Leonid meteor storm using intensified video cameras
as well as meteor radar systems showed significant
fluctuations of the activity. Applying a wavelet
analysis to the data it is shown that we see
quasi-periodic variations with a typical period of
7 minutes. Given the geocentric velocity of the
Leonid meteoroids, this hints at structures within
the stream at a scale of about 30000 km along the
Earth's passage, or about 9000 km vertical to the
stream's plane. As the distance between the
observing sites at which such fluctuations were
recorded is of the order of several 1000 km in N-S
and E-W direction, the variations should reflect a
characteristic of the stream. Similar observations
are only possible during meteor storms in order to
collect a sufficient sample within 2 minutes or
less. 2.5
Bolide Fragmentation Modeling
Douglas O. ReVelle (Los Alamos National
Laboratory, Los Alamos, New Mexico 87545, USA)
In this talk we extend work begun at the Cornell
ACM meeting. The shape change parameter is
evaluated for conditions when it is negative. For
the values of the shape change parameter between 0
and 2/3, ablation, shape change and deceleration
can occur. For values < 0, however, large
lateral growth of the body occurs. This negative
region of the shape change parameter corresponds to
the flight regime that was "rediscovered" by Hills
and Goda and by Chyba, Zahnle and Thomas in the
1990's and analyzed in detail by Grigoryan in the
1970's. We have determined analytic expressions for
the shape change parameter (assuming a constant
ablation parameter and constant meteoroid velocity)
and for the fragmentation scale height, Hf. We have
evaluated Hf assuming that fragmentation was
triggered if the stagnation pressure exceeded the
body's compressive/tensile strength. If Hf >>
H, the density scale height, the single-body
approximation is applicable, whereas, if Hf
<< H, catastrophic, pancake break-up will
occur. In the limit with the shape change parameter
< 0 with very small ablation, large increases in
the frontal cross-sectional area are predicted to
occur, but only over a very limited range of
conditions. In addition, as the shape change
parameter becomes progressively more negative, end
heights raise substantially. We also evaluate the
effect of a negative shape change parameter on
light emission so that a nearly complete,
self-consistent model of the bolide phenomena can
be formulated. PSB-12
Bolide Luminosity Modeling: Comparisons between
Uniform Bulk Density and Porous Meteoroid
Models
Douglas O. ReVelle (Los Alamos National
Laboratory, Los Alamos, New Mexico 87545, USA)
We compare predictions of normalized bolide
luminosity for two fundamental bolide models, one
assuming a uniform bulk density throughout the body
and a second which assumes a uniform chondritic
composition throughout, but with varying amounts of
porosity (assumed to be filled with either
water-ice or open space). The second model is based
upon the uniformity of spectral observations taken
over many years during periods of shower meteors
from the extremes of the Geminids to the
dustball-like Draconids. The first model utilized
is due to ReVelle (1979, 1993) and the second is
based upon the porous meteoroid model of ReVelle
(1983, 1993). The standard, uniform bulk density,
ablation model assumes that the drag and heat
transfer area are equivalent in the positive, shape
change factor limit. For porous meteoroids however,
the heat transfer area can exceed the drag area by
increasingly larger amounts as the body's porosity
increases. ReVelle (1983) used this approach to
show that the bulk density and ablation parameter
compositional group identifications of Ceplecha and
McCrosky (1976) were essentially correct. When
these factors are introduced into the relevant
model equations, a set of nearly self-consistent
predictive relations are developed which readily
allows comparisons to be made of the end-height
variations and of the normalized luminous output of
the two basic types of meteoroid models. PSB-13
Infrasonic Monitoring of the Global Influx Rate
of Large Bolides
Douglas O. ReVelle (Los Alamos National
Laboratory, Los Alamos, New Mexico 87545, USA)
We have utilized recent infrasonic bolide
observations to estimate the large bolide influx
rate. These infrasonic signals are from the
densest, most deeply penetrating objects entering
the atmosphere. Undoubtedly, depending on the exact
mass range under consideration, the total influx is
about a factor of five-ten times greater. This work
is a continuation or work shown at the Cornell ACM
meeting in 1999 and initiated by Wetherill and
ReVelle in the late 1970's using data from AFTAC
(Air Force Technical Applications Center, Patrick
AFB, Florida). There have been several additional
large bolides detected infrasonically since 1999
that are included in our latest evaluation of the
global influx rate of large bolides. Some of these
have also been detected independently by US DoD
Satellites. Thus, in some cases we also have
independent estimates of the bolide source energy
that can be used for an evaluation of the accuracy
of the infrasonic source energy estimate. We have
also used statistical counting error procedures to
estimate the uncertainty in the influx rate as a
function of the source energy, assuming that the
source energy estimates are without error. For
example, at a source energy of 0.2 kt (1 kt = 4.185
x 10(12) joules), we find a global influx rate and
its estimated uncertainty of 28.1 (+/-8.9) bolides
per year. 8.3
Leonid Entry Modeling: Application to the Bolide
of November 17, 1999
Douglas O. ReVelle (Los Alamos National
Laboratory, Los Alamos, New Mexico 87545, USA)
The results of ReVelle (AIAA Aerospace Sciences
Conference, Reno, Nevada, January, 2000) are
compared against atmospheric observations of the
Leonid fireball of 11/17/1999 in northern New
Mexico (NM). These included observations at the
Phillips Laboratory Starfire Optical Range (USAF
facility) near Albuquerque of the so-called
"glow-worm" persistent train which could be tracked
for ~1 hour, intensified CCD camera records at
Placitas, NM, by all-sky video camera records and
infrared radiometers at Sandia National Laboartory
in Albuquerque as well as by 2 ground observers in
the town of Los Alamos. This bolide was also
detected infrasonically at Los Alamos National
Laboratory at the CTBT, IMS (Comprehensive Test Ban
Treaty, International Monitoring System) prototype
array by ReVelle and Whitaker (Meteoritics, 2000).
We compare model predictions of velocity, mass,
blast wave radius, wave frequency, etc. as a
function of the initial source energy against the
results predicted using the infrasonic wave
arrivals and their properties at the ground
(amplitude, wave period, duration, etc.) at the
observed slant-range from the bolide. The
infrasonic signals were analyzed using the basic
line source model of ReVelle (1976) and were
independently shown to have emanated from a height
region near the Mesopause where the bolide
explosively ended its visible flight, presumably
due to its low material strength. PSA-15
[To top of page]
Theoretical Entry Modeling of Large Leonid
Bolides
Douglas O. ReVelle (Los Alamos National
Laboratory, Los Alamos, New Mexico 87545, USA)
We have used the entry model of ReVelle (1979)
using an energy of ablation/unit mass for
vaporization for weak cometary meteoroids of 3.8
MJ/kg (Jessberger et. al., 1988). These model
predictions have been combined with the energetics
model of ReVelle (1993). The energetics model has
been calibrated using the flight data from the
Pribram, Lost City and Innisfree meteorites where
ReVelle (1980) determined that at the observed end
height about 1 % of the kinetic energy of the
original body remained. If the above estimate of
the value of the energy of vaporization/kg of
cometary meteoroids is reduced by a factor of 5,
very good agreement is obtained between the
theoretical, equilibrium flow, entry model and the
observed ablation parameter (0.10-0.21 kg/MJ,
personal communication with P. Spurny, 2000) for
large, low density, Leonid meteor-fireballs.
Predictions of the expected laminar and turbulent
convective heat transfer and of the radiative heat
transfer coefficients (regardless of the gas cap
opacity) are made using entirely analytic
expressions that were developed. These expressions
allow a prediction of the velocity, the ablation
parameter, the percentage mass loss and of the
Knudsen number, etc. to be made. In addition,
values of the line source, nonlinear blast wave
relaxation radius and of the associated infrasonic
wave frequencies are also determined. 2.4
On the Relationship between Asteroids, Fireballs
and Meteorites
A.E. Rosaev (FGUP NPC NEDRA, Yaroslavl,
Russia)
Best of interest searching for parental bodies
for meteors, fireballs and meteorites with well
determined orbits. We use two days to study this
problem in this work. First way &emdash;
investigation close orbits by one of number of
empirical criteria like criterion
Southworth-Hawkins. The second way is to study the
orbit intersection statistics. The fireballs of
Prairie network and meteorites with well determined
orbits was took into account. Obviously, that
fireballs and meteorites &emdash; an essence of
bodies, having potentially unstable orbits and, as
an effect, small lifetimes. If take sufficiently
natural suggestion on that, that similar objects
are form in collisions NEA with each other and with
comets, possible expect that crossing the orbits of
asteroids and fireballs, or meteorites will
indicate us on the most close on a time events of
mutual collisions NEA. Really, the distribution
nearly intersected orbits in the system
NEA-fireball and fireball-fireball show significant
non-homogenous. Possible select about 10 areas to
concentrations the cross points of orbits of
fireballs and NEA. Probably, they correspond to the
most recent disastrous events. Results of
calculations for meteorites Lost City, Prhibram,
Innisfree Peekskill and Tun-guska's is given. In
case of a general conclusion of this work, the
hypothesis of an very close relation studied
meteorites with NEA put forward. 8.2
Asteroid (1620) Geographos as a Possible Parent
Body for a Meteor Stream
G.O. Ryabova (Research Institute of Applied
Mathematics and Mechanics, Tomsk, 634050, Russia.
e-mail: astrodep@niipmm.tsu.ru)
The study was undertaken to answer the following
questions: when and how particles could escape from
the asteroid, could they reach the Earth and could
we detect some of them in available meteoroid orbit
databases. It was found that the rotational
acceleration does not exceeds the gravitational one
for all possible rotational states. So the escape
of particles from the asteroid apparently took
place during a close approach with the Earth (plus
tidal forces) or in a collision. Numerous model
streams having different schemes and times of
ejection were considered. It was obtained that
model meteoroid streams ejected with high
velocities (up to 1 km/s) can approach the Earth's
orbit twice, once before (February-March) and once
after (August) perihelion. There were found 44
correlated meteor orbits (in databases containing
> 75000 orbits) from the both showers and a
taxon structure was derived for them. The
distribution of ejection velocity vectors looks
like originated at impact of a catching up small
body, but the time of the collision remains
unknown. So, with the high probability Geographos
is the parent body for a meteor stream, generating
twin meteor showers observable at the Earth :
Spring and Summer Geographides. 1.10
Mathematical Model of the Geminid Meteor Stream
Formation
G.O. Ryabova (Research Institute of Applied
Mathematics and Mechanics, Tomsk, 634050, Russia.
e-mail: astrodep@niipmm.tsu.ru)
The Geminid meteoroid stream formation and
evolution was studied by the method of nested
polynomials. Besides other results the present work
puts forward a new theory to explain the secondary
maximum of the Geminid rate profile: branches of
the stream have been formed due to differences in
orbital parameters of particles ejected from the
cometary nucleus before and after perihelion. The
model stream originated in such a way has a
distinguishing feature: the smaller meteoroid mass,
the greater the distance between maxima. Their
relative positions depend on the stream age. If the
stream is young then as meteoroid mass increases
the every next pair of maxima appears to be
enclosed in the previous one. (Like a Russian doll
"matrioshka"). Such is indeed the case of the
Geminids. So we have a weighty argument in favour
of the cometary past of the asteroid Phaethon (the
parent body). A comparison of the model and
observed rate profiles allowed to propose a
hypothetical scenario of the comet disintegration:
greater intensity of dust production before
perihelion, significant change of the cometary
orbit due to jet forces and ejection of dust in the
wide cone directed to the Sun. PSA-2
Detection of Interplanetary and Interstellar
DUST particles by Mars Dust Counter (MDC) on Board
NOZOMI
Sho Sasaki (1), Eduard Igenbergs and Gerd
Hofschuster (2), Hideo Ohashi (3), Walter Naumann
(4), Ralf Muenzenmayer (5), Eberhard Gruen (6),
Yoshimi Hamabe (1), Heinrich Iglseder (7), Georg
Farber and Franz Fischer (2), Akira Fujiwara (8),
Tohru Kawamura and Ken-ichi Nogami (9), Tadashi
Mukai (10), Håkan Svedhem, Gerhard Schwehm
and Ingrid Mann (11)
1) Univ. Tokyo; 2) Technical Univ. Munich; 3)
Tokyo Univ. Fishery; 4) Kayser-Threde GmbH; 5)
Daimler-Benz Aerospace; 6) MPI-Kernphysik; 7)
Wilkhahn; 8) ISAS; 9) Dokkyo Univ. Medicine; 10)
Kobe Univ.; 11) ESA-ESTEC.
Mars Dust Counter (MDC) is an impact-ionization
dust detector on board the Japanese Mars mission
NOZOMI, which was launched on 1998-07-04. It is an
improved type of MDC-HITEN and MDC-BREMSAT and has
three detection channels (electron, iron, and
neutral) to discriminate noise signals from impact
signals. The main aim of MDC is to reveal the
predicted Martian ring or torus of dust from Phobos
and Deimos. On 1998-11-18, NOZOMI encountered the
Leonids meteoroid stream. MDC detected two dust
impacts, but directional analysis showed that those
particles probably did not belong to the Leonids.
However, the detected dust number in November 1998
was apparently higher than in other months. Leonids
meteoroid stream would have increased the dust
population around the Earth, probably though
collisions of stream particles with the Moon.
NOZOMI orbital plan was changed; Mars insertion was
postponed to be on 2004-01-01. Between 1999 and
2003, MDC-NOZOMI continuously measures the dust
environment between the Earth's and Martian orbits.
By the end of 2000, MDC had detected more than 60
events of dust impact. From the analysis of
velocity and direction of particles, those events
should include maybe five particles of interstellar
origin. 10.7
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Observations on
Stratospheric-Mesospheric-Thermospheric
Temperatures Using Indian MST Radar and Co-located
LIDAR during Leonid Meteor Shower (LMS)
R. Selvamurugan (1) , C.V. Devasia (2), A.R.
Jain (1), C. Raghava Reddi (2).P.B. Rao (1) and R.
Sridharan (2)
1) National MST Radar Facility, Tirupati, 517
502, India; 2)Space Physics Laboratory, Vikram
Sarabhai Space Centre, Trivandrum 695 022,
India
The temporal and height statistics of the
occurrence of meteor trails during the Leonid
meteor shower revealed the capability of the Indian
MST radar to record large number of meteor trails.
The distribution of Radio meteor trails due to
Leonid meteor shower in space and time provided a
unique opportunity to construct the height profiles
of lower thermospheric temperatures and winds with
good time and height resolution. There was a
four-fold increase in the meteor trails observed
during the LMS compared to a typical non-shower
day. The temperatures were found to be in excellent
continuity with the temperature profiles below the
radio meteor region derived from the co-located
Nd-Yag LIDAR and extend the maximum height of the
temperature profile from the LIDAR to ~110 km.
There are however some significant differences
between the observed profiles and the CIRA-86 model
profiles. The first results on the meteor
statistics and neutral temperature are presented
and discussed below. PSA-26
The Result of 1999 Leonids Daytime Observation
in Japan
Hirotaka Serizawa and Masayuki Toda
The large appearance of Leonids was observed in
Europe on November 18 in 1999 at the 2:00UT
(11:00JST). Then, daytime-meteor was detected some
observers in each place, and the number of 40
meteors were detected in 4 hours in Japan. Since
globally daytime-meteor observation is rare most
people would have doubt about the objectivity of
data. Therefore, I tried to identify with each
Radio Meteor Observation, in order to acquire the
objectivity of data. Consequently, four shooting
stars were in accorded with the result of Radio
Meteor Observation. Besides, two synchronous
meteors were observed by two observers. Therefore,
these meteors could be reliable. However, there
were few bright (shooting stars>-5 magnitude)
which could be observed in Europe in daytime at the
same time. For that reason, the question arose in
the luminous intensity of the meteor that we
observed. As one of this cause, it can be
considered that the meteor luminescence mechanisms
differ daytime from night. I would like to call
more observers all over the world to carry on
meteor observation from now on to collect the data
about a daytime-meteor. PSA-18
The Discrete Solution of a Quasi-thomography
Problem for Construction of the Radiant
Distribution of Meteors by Results of Radar
Goniometer Measurements
Vladimir Sidorov and Sergey Kalabanov
A new solution of the quasi-tomographic
determination of the spatial distribution of the
meteoric complex as constructed from radar
goniometer data is represented for the first time.
A previous solution obtained by O. Belkovich,
V.Sidorov and T. Filimonova was based on the
assumption of a continuous radiant distribution of
sporadic meteors on the celestial sphere. In that
theory, the number of unknowns grew quadratically
with increase of the angular measurement accuracy.
Therefore a stable solution was possible only for
the angular measurement accuracy in 10 x 10 deg
bins. The new solution is obtained using the
hypothesis that there is a discretization in the
angular radiant distribution of meteors. It assumes
the meteor flux consists, not of an ensemble single
meteors, but consists of a system of showers and
microshowers with close velocities and close
angular grouping. The new method uses a computer
optimization of such a radiant distribution on the
celestial sphere subject to constraints of the
microshower hypothesis, the mirror condition of
trail reflection and other independent
measurements. The method is implemented on a
computer for routine goniometer processing with
discrete 2 x 2 deg bins and has been used for
determination of meteor shower orbit parameters on
one day of radar observation, December 13, 1986.
1.4
Microswarm Structure of a Meteoric Complex
outside of a Plane of an Ecliptic
Vladimir Sidorov, Sergey Kalabanov and Tamara
Filimonova (Kazan University)
Earlier we noted that the radiant distribution
of sporadic meteors obtained by the radar
tomography method shows stable structures of
radiants distributed along at particular elongation
angles from the apex. In the present activity we
have tried to find out (a) how these structures
vary in the course of the year, (b) how they are
correlated in time, and (c) whether they will be
repeated from one year to the next.
Nearly continuous radar observations of the
meteors from Kazan during January-April and
June-December 1993; during 3 different years in
April (1987, 1988 and 1993); and in December
(1986-1988) were analysed by a quasi-tomographic
method with a bin size of 10 x 10 deg. We have
discovered that a toroidal structure dominates
February to April. During August to October, on the
contrary, a stable minimum is found in the
neighbourhoods of ± 90 deg to ecliptic plane.
The apparent distributions of meteors at different
angles to the cliptic plane during April for
different years are very close and mostly break up
into three maxima at 75, 90 and 115 deg. The data
of December and April were analysed additionally by
a discrete quasi-tomographic method with a 2 x 2
deg bin of radiant position. The role of showers
and microshowers in the formation of local stable
structures in the total radiant distributions of
meteors and a small comet origin of some of the
observed microshowers is discussed. PSB-17
Radar Observations of the 1999 and 2000 Leonid
Meteor Storms at Middle Europe and Northern
Scandinavia
Werner Singer (1), Nicholas J. Mitchell (2) and
Johannes Weiss (1)
1) Leibniz-Institut fuer Atmosphaerenphysik,
18225 Kuehlungsborn, Germany; 2) Department of
Physics, University of Wales, Ceredigion SY23 3BZ,
UK
Observations of the 1999 and 2000 Leonid meteor
storms made with all-sky meteor radars in Middle
Europe (54N) and northern Scandinavia (68N) were
analyzed in terms of height-dependend meteor rates
and entrance velocities. The 1999 Leonid meteor
storm is characterised by a major activity peak on
November 18 at 2h5m UT with a peak rate of about
1400 meteors/h. In contrast to the 1999
observations, we found three activity maxima for
the 2000 Leonid storm. The first peak (170
meteors/h) was observed on November 17, 2000, at
8h15m UT related with the 1932 Leonid dust trail.
The second well pronounced maximum (130 meteors/h)
was detected on november 18 at 7h25m UT associated
with the 1866 Leonid dust trail. The third broad
activity event (about 70 meteors/h on average) was
found on November 18 between 1h UT and 5h UT
related with the 1733 Leonid dust trail. During
both years the Leonid storm activity was dominant
at altitudes above 98 km. PSA-25
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Common Ground-based Optical and Radiometric
Detections of Fireballs within the Czech Part of
the European Fireball Network
Pavel Spurny (Astronomical Institute, Academy of
Science, Ondrejov Observatory 251 65 Ondrejov, The
Czech Republic) and Richard E. Spalding (Sandia
National Laboratories, PO Box 5800, Albuquerque, NM
87185-0978, USA)
Since August 1999 two radiometric systems
equiped with optical sensors are operated at two
stations of the Czech part of the European fireball
network (EN). During this period we have obtained
several very detailed lightcurves for bright
fireballs recorded also photographically in scope
of the EN. First results of this study will be
presented. PSB-15
The EN310800 Vimperk Fireball: Probable
Meteorite Fall of an Athen-type Orbit Meteoroid
Pavel Spurny and Jiri Borovicka (Astronomical
Institute, Academy of Science, Ondrejov Observatory
251 65 Ondrejov, The Czech Republic)
We report a detection of an unique fireball
photographed at two Czech stations of the European
Fireball Network. This slow-moving fireball with
initial velocity of only 15 km/s reached the
maximum absolute brightness -14 and penetrated down
to almost 20 km. The meteorite fall of several
pieces of the total mass of several kilograms is
highly probable. However, no meteorite has been
recovered yet. From one very rough spectral record
and also from its behavior in the atmosphere we
found that it was stony meteoroid, probably
ordinary chondrite. The main exceptionality of this
fireball is in its heliocentric orbit, with
semimajor axis only 0.8 AU, eccentricity 0.3,
aphelion 1.03 AU and inclination 17 degrees. This
rare Aten type orbit is only third one in the
history of decades-long operation of the European
Fireball Network. PSB-16
New Type of Radiation of Bright Leonid Meteors
above 130 km
Pavel Spurny, Pavel Koten (Astronomical
Institute, Academy of Science, Ondrejov Observatory
251 65 Ondrejov, The Czech Republic), Hans Betlem,
Klas Jobse and Jaap van't Leven (Dutch Meteor
Society, Lederkarper 4, 2318 NB Leiden, The
Netherlands)
Precise atmospheric trajectories of very bright
Leonid meteors have been determined from the
double-station photographic and video observations
of Leonid meteors in scope of the ground-based
expedition to China during the exceptional
so-called "fireball night" of 1998 November 16/17.
Whereas beginning heights of photographed meteors
are all lower than 130 km, those observed by the
all-sky video system or by the even more sensitive
LLTV system were recorded up to 200 km for the
brightest Leonids meteors. Such high beginnings for
meteors have never before been observed. All cases
with beginnings recorded by sensitive LLTV systems
exhibit comet-like diffuse structures with sizes on
the order of kilometers that developed quickly
during the meteoroids descent through the
atmosphere. For the brightest event with maximum
absolute magnitude of -12.5, we observed an arc
similar to a solar protuberance and producing a jet
detectable several kilometers sideways from the
brightest parts of the meteor head, and moving with
a velocity over 100 km/s. These jets are common
features for all studied very high altitude
meteors. When these meteoroids reached 130 km
height, their diffuse structures of the radiation
quickly transformed to the usual meteor appearance
resembling moving droplets, and meteor trains
started to develop. Recently we observed similar
behavior for two Eta Aquarid, one Perseid and one
Lyrid meteors with beginning heights up to 150 km.
These meteor phenomena above 130 km were not
recognized before our observations, and they cannot
be explained by standard ablation theory. 2.2
Double station TV Meteors and Analysis of their
Trajectories
R. Stork, P. Koten, J. Borovicka, P. Spurny and
J. Bocek (Astronomical Institute, Academy of
Sciences of the Czech Republic, CZ&endash;25165,
Ondrejov, Czech Republic)
The TV observation of meteors is performed in
Ondrejov since 1990. Together with taking meteor
spectra we started also double station observations
in the integral light in 1997. The stations are
located in Ondrejov and Kunzak, it gives the base
distance of 92.5 kilometers. We use camcorders with
image intensifier, the diameter of the field of
view is about 20 degrees, limiting magnitude about
8 for stars and 6&endash;7 for moving object
(meteor). Hundreds of shower and sporadic meteors
were recorded, about half of them are double
station ones. The selected meteors were measured on
digitized records from both stations and their
trajectories in the atmosphere and heliocentric
orbits were computed. Also K_B parameter
[Ceplecha Z. 1988, Bull. Astron. Inst.
Czechosl. 39, p. 221&endash;236] was computed
for meteors and the distribution of shower and
non-shower meteors into classes using that
criterion will be presented. 4.4
The Dispersion of the Swarm of Fragments of
Large Meteoroids due to Aerodynamic Forces
Yang Su (Beijing Astronomical Observatory and
National Astronomical Observatories, Chinese
Academy of Sciences, Beijing, 100012)
In order to gain insight into the dispersion of
the swarm of fragments due to differential
atmospheric pressure across it, I derive an
approximate analytic solution to the simple
analytic model of lateral spreading of the
cylinder-like swarm of fragments in which
gravitational acceleration and ablation are
neglected. The solution is applicable to the
initial fragmentation stage of large meteoroids
above several meters in size. Because the spreading
of fragments from the initial fragmentation stage
defines the primary ellipse of strewn field, this
solution is applied to the scatter ellipses of
meteorite showers. In comparison to a simple
analytic approximation to airburst altitude, my
solution demonstrates that the growth of the
effective cross-sectional area of the swarm in the
initial fragmentation stage is well below the one
at airburst altitude. The initial fragmentation
stage should never occur at airburst altitude
unless the meteoroid begins to break up at an
altitude less than 2.8 H and airburst at an even
much lower altitude, where H is the scale height of
the atmosphere. 5.2
Dust Measurements in the Geostationary Orbit
Håkan Svedhem and Gerhard Drolshagen
(ESA/ESTEC, PB 299, NL-2200AG Noordwijk, The
Netherlands; e-mail: h.svedhem@esa.int and
gerhard.drolshagen@esa.int) and Eberhard Gruen (MPI
f Kernphysik, D-69029 Heidelberg, Germany; e-mail:
eberhard.gruen@mpi-hd.mpg.de)
The impact detector GORID, on the Russian
Express II satellite has now collected data on
Cosmic Dust and Space Debris for more than four
years from its geostationary location at first 80
and later 103 deg East. During this time a large
number of events have been registered and these are
now being analysed and categorised. The yearly
average number of certain impacts has varied from
1.7 per day to 3.2 per day. Recent re-calibration
of a spare model has resulted in more accurate
factors for conversion of the measured parameters
into physical parameters as particle mass and
velocity. Data sets from one or several full years
are used to suppress the possible biases that can
result from spatial, temporal and directional
variations in the flux and to reduce the
statistical errors. During several occasions
particles have been detected clustered in time,
with up to 30 or more particles within one hour. In
addition, at some dates these clusters have been
detected at the same times for several consecutive
dates. We believe these particles are related to
exhaust particles from the solid rocket boosters
used for changing the geostationary transfer orbit
into a geostationary orbit. For the remaining
particles the majority seems to be natural
meteoroids. 10.10
[To top of page]
A Fine Structure of Perseid Meteoroid Stream.
Method of Indices
J. Svoren (1), V. Porubcan (2) and L. Neslusan
(1)
1) Astronomical Institute of the Slovak Academy
of Sciences, SK-059 60 Tatranska Lomnica, The
Slovak Republic; 2) Astronomical Institute of the
Slovak Academy of Sciences, Dubravska 9, SK-842 28
Bratislava, The Slovak Republic
A procedure based only on mathematical
statistics is used to study the fine structure of
the Perseid stream and its filaments which cannot
be reliably separated by iteration methods. Besides
the five orbital elements incorporated in the
Southworth-Hawkins D-criterion, we also take into
account the coordinates of the radiant which belong
to the most precisely determined parameters and the
geocentric velocity as a significant parameter
characteristic for physically related orbits. The
basic idea of the procedure is a division of the
observed ranges of parameters into a number of
equidistant intervals and assignment of indices to
a meteor according to the intervals pertinent to
its parameters. The meteors with equal indices are
considered for mutually related. Since various
parameters listed in the catalogue contain various
relative errors, it is necessary to use different
numbers of intervals in the division of each
parameter to obtain a good fit with the real
orbital distribution. The relative ratios,
approximated by small integers, corresponding to
the reciprocal values of the relative errors of
parameters, are applied as the basic numbers for
the division of the parameters. Our results are
compared with the known filaments of the Perseid
meteoroid stream discovered by other authors.
PSA-7
Spectroscopic Analysis of Fine Structures in
Leonids
Toshio Tsukamoto (Nagoya university), Shinsuke
Abe (Institute of Space and Astronautical Science),
Noboru Ebizuka (The Institute of Physical and
Chemical Research), Hajime Yano (Institute of Space
and Astronautical Science), Yasuhiro Hirahara
(Nagoya university) and Jun-ichi Watanabe (National
Astronomical Observatory)
Observations of meteors and the orbital
caluculations lead to understanding behavior of
cometary dust grains in space. Spectroscopic
obserations of meteors enable us to investigate not
only the chemical composition of meteors but also
the chemical heterogeniety among the meteor dust
trails (fine structures) . However, there had not
been enough data to understand fine structures in a
meteor shower until the 1999 Leonids.
55P/Tempel-Tuttle, the parent comet of the Leonid
stream, returns to perihelion every 33 years,
generating a new trail of dust each time. During
the 1999 Leonid meteor storm, the Earth encountered
various trails which allowed us to study the fine
structure between those dust trails generated in
different perihelion epochs. We report results of
those fine structures within the 1999 Leonids.
These observations were carried out using Grism as
slitless spectrometer with an image intensifier.
The images were recorded on NTSC video at a rate of
30 frames per second, with 37.1 x 20.8 deg, FOV.
The main peak occurred around 2hUT while sub-peaks
stood out around 1h30m, 1h45m, 2h15m, 2h20m, 3h00m
UT on 18 November 1999. We examine the temporal
spectroscopic differences among those fine
structures. PSA-22
Results of Double-station TV Obsevations during
1998 and 2000
Masayoshi Ueda (Nippon Meteor Society), Yasunori
Fujiwara, Masatoshi Sugimoto (Nippon Meteor
Society)
We carried out double-station TV meteor
observations during 1998 and 2000. The TV
observations could record faint meteors. The
radiant positions of Leonid and Taurid meteors was
determined. PSA-28
Results of Foward-Scatter Radio Observations
Masayoshi Ueda (Nippon Meteor Society) and Kimio
Maegawa (Fukui National College of Technology)
Our radio meteor observation uses its own 50W
continuous wave beacon on 53.750MHz in 6m amateur
band with a broad directivity antenna. The location
of transmitter is Fukui, Japan (Longitude 136.18
degrees E, Lattitude +35.93 degrees N). The
location of receiver is Osaka, Japan (Longitude
135.64 degrees E, Lattitude +34.53 degrees N).
Though the distance between Fukui and Osaka is
about 200km, we could detect about 1,500 meteor
echoes in no shower day. We report the mean daily
variation of meteor rates and The mean annual
variation of meteor rates. PSB-1
The New Meteorite Radar of the Sodankylä
Geophysical Observatory
Thomas Ulich (1), Markku Lehtinen (1), Antero
Väänänen (1), JuhaPirttilä 2),
Markku Markkanen (1) and Jyrki Rahkola(2)
1) Sodankylä Geophysical Observatory,
Sodankylä, Finland; 2) Invers Ltd.,
Sodankylä, Finland
At the Sodankylä Geophysical Observatory
(67° 22' N, 26° 38' E) a new meteorite
radar was built during the winter 2000/01. The
radar employs a new antenna geometry minimising the
directional ambiguities of the received echos.
Furthermore, the 8-channel radar does not only
sample the received signals but also the
transmitted pulses in order to get an accurate
picture of their shapes. The transmitted pulses are
sampled with all 8 channels allowing for
calibration of the receivers on a pulse-to-pulse
basis. In June 2001 test operations began. Here we
present the new instrument and some first results.
PSB-7
The Complex of Asteroids, Comets and
Meteoroids
Yu.I. Voloshchuk and B. L. Kashcheev (Kharkiv
State Technical University of Radioelectronics,
Lenin av., 14, Kharkiv, 61166, Ukraine)
A global structure of the asteroid, comet, and
meteoroid complex and its origin is the objective
of this paper. The problem of
meteoroid-comet-asteroid evolution is considered on
the basis of modern studies of small bodies in the
Solar system. Along with major planets and their
satellites, the Solar system contains small bodies:
asteroids, comets, meteoroids and their complexes.
The bodies of these complex are in the state of
active evolution by perturbing forces, in contrast
to the stable systems of major planets and their
satellites. Another common feature of the bodies of
the complexes is their ability to fall to many
parts and to disintegrate. In addition, their
orbits pass partly through the same domains of
interplanetary space. There are classic the Taurid
asteroid complex, the complex of the Halley comet
with Aquarid and Orionid streams and many other
complexes in the Solar system. In general one
complex can include: several comets, several
asteroids and several decades of meteor streams.
Using one of the largest meteor data banks and the
results of calculation of asteroid orbit evolution,
new approaches to the search for space bodies that
may be the parents' bodies of the meteor streams
are formulate. More than 230000 individual orbits
of meteoroids with masses exceeding 10-6 g were
registered by the meteor automatic radar system
(MARS) from January 1972 till December 1978 in
Kharkiv. 159787 individual orbits were chosen
according to special technique to increase further
analysis reliability. The technique for selection
of streams and associations from a large sample of
individual meteor orbits is used. The investigation
were made on the different samples from observation
material, which volume is more than 5 thousands
minor meteor showers of this unique Kharkiv
electronic orbit catalogue. PSB-19
[To top of page]
Differential Ablation of Meteoroids as Observed
by Ground-based Lidars
Ulf von Zahn and Josef Hoeffner
(Leibniz-Institute of Atmospheric Physics, 18225
Kuehlungsborn, Germany), Edmond Murad (Air Force
Research Laboratory, Hanscom AFB, MA 01731, U.S.A.)
and William J. McNeil (Radex Inc., Bedford, MA
01730, U.S.A.)
We report on an extensive set of new
observations of meteor trails by ground-based
lidars. The observations are performed with metal
resonance lidars which sound the atom densities of
Na, K, Fe, Ca, and Ca+ in the altitude range
between 80 and 105 km. At the Leibniz-Institute of
Atmospheric Physics we have clustered three such
lidars at one site for simultaneous common-volume
observations of meteor trails. We have also
enhanced our lidar observations of meteor trails
through co-located observations of meteors by an
image-intensified video camera.
The average rate of trail detections is 0.8
meteor trails per hour of lidar observations. The
total number of our lidar-observed meteor trails
stands at more than 1300. We show through
observations and modelling that the capability of
any lidar to detect meteor trails is strongly
altitude dependent. We estimate that Leonids must
have a brightness < +7 m (equivalent photometric
mass 0 micro g, diameter 0.35 mm) to become
detectable for our lidars.
The most important result of our research is the
discovery that lidar-observed meteoroids ablate
almost exclusively differentially. Differential
ablation shows up in the unexpectedly small number
of two- and three-element trails in comparison to
that of single-element trails (of 1279 analyzed
trails, only 42 trails are two-element trails and 6
are three-element trails) and the lidar-measured
ratios of metal abundances in meteor trails (all
averages of the various abundance ratios deviate
significantly from CI chondritic composition). The
preponderance of differential ablation for
meteoroids with masses in the milligram-to-gram
range could indicate that a very large percentage
of all meteoroids desintegrate into many tiny
particles in the early part of their atmospheric
entry. 4.2
The Activity Profile of Comet 55P/Tempel-Tuttle
in 1998 return: Meteoroid Release Concentration on
the Perihelion
J. Watanabe (Nat. Astron. Obs.Japan), H.
Fukushima (Nat. Astron. Obs. Japan) and T. Nakamura
(Canon Co. Ltd)
It is important to know the activity profile of
the parent comets of meteor showers. The activity
of the parent comet of the Leonids,
55P/Tempel-Tuttle had never been followed until the
recent return in 1998 mainly due to the geometrical
difficulty of its orbit relative to the Earth. We
carried out a CCD imaging monitor of this comet
from January through February in 1998 by using
50-cm telescope of National Astronomical
Observatory, Japan. The circular shape of the coma
was not changed during this period for the
pre-perihelion phase. The photometric measurements
of the coma indicated high dependency of the
activity on the heliocentric distance, of which the
parameter index n is derived as about 10. This
large value indicates that the dust release from
comet 55P/Tempel-Tuttle is concentrated at around
the perihelion passage. PSA-14
Interferometric Radar Observations at Widely
Separated Locations
A.R. Webster, J. Jones, K.J. Ellis and M
Campbell (The University of Western Ontario,
London, Canada), M.A. Abdu, P Batista and B.
Clemesha (Instituto Nacional de Pesquisas Espaciais
Sao Paulo, Brazil)
Back-scatter radars have been operated
simultaneously and on a continuous basis at
Tavistock, near London Canada and near Sao Paulo,
Brazil. Each system consists of five separate
receiving antennas arranged as two orthogonal
3-element arrays that allows the unambiguous
determination of the direction in space of the
meteor echo relative to the station location. The
antennas used are two-element Yagi type with
horizontal elements and pointed vertically upwards
to give all round coverage. Aside from the
operating frequency, 29.3MHz in Canada and 35.2MHz
in Brazil, the systems are identical. Results from
these operations during the time of the 1999
Geminids are presented illustrating the
similarities and differences arising from the
significantly different site coordinates. 6.3
The Determination of the Ejection Velocity of
Meteoroids
I.P. Williams (Faculty of Engineering and
Mathematical Sciences, Queen Mary, University of
London; e-mail I.P.Williams@qmw.ac.uk)
A knowledge of the ejection velocity of
meteoroids from the nucleus of a parent comet is
important both for an understanding of processes
ongoing in cometary nuclei and the accurate
modelling of the evolution of the resulting stream.
However, determination of this from the
observations of comets tends to be difficult, since
observational techniques focus on grains of sizes
that are different from meteoroids. Similarly,
determination from the study of meteor showers is
also difficult because the properties of the
observed meteor shower are generally affected by
post-ejection evolution through the effects of
radiation and planetary perturbations. Thus in
order to make deductions regarding the meteoroid
ejection velocity from the study of meteor showers,
we must a) find a shower that is so young that
evolutionary effects are ignorable or b) find a
stream where evolution is unimportant or c) we must
find a shower that has some special characteristic
whose appearance is very sensitive to the ejection
velocity. The aim of this talk is to discuss these
three options and compare the results so obtained.
1.6
Prediction and Observations of Leonid Meteor
Shower in China
Guang-jie Wu (Yunnan Observatory, Chinese
Academy of Sciences, Kunming 650011, and National
Astronomical Observatories, Chinese Academy of
Sciences, Beijing 100012) and Guang-yu Li Yue-hua
Ma (Purple Mountain Observatory, Chinese Academy of
Sciences, Nanjing 210008, and National Astronomical
Observatories, Chinese Academy of Sciences, Beijing
100012)
Recent years, Leonid meteor shower has been paid
more attention in China. Observations by both
visible and radio have been performed under the
organizing of Chinese Leonid Watch. We have
observed some interesting phenomena, like the
filamentary structure of the shower, the variations
of the size distribution of meteoroids and the mass
density. In 1998, Chinese and Dutch astronomers in
Qinghai firstly observed an activity of very bright
fireballs; in Xinxiang, we observed the expected
main shower with radar, and the radio peak was as
high as 2500 hr-1; in Yunnan, the records indicated
that the contour of the peak maximum is asymmetry.
An abnormal peak in the ionosphere characteristic
value was also detected about 18 hours after the
main shower. In 1999 and 2000, the observations
were still obtained greatly. From observed
differences between the longitude of the ascending
node of meteoroids and that of their parent comet,
we find this difference depends on the ejection
position as well as the ejection velocity. We
successfully predicted the Leonids in 1999 and 2000
with a T_{E-C} versus CEOS diagram. We are working
on the research of the orbital evolution of the
meteoroid stream with the calculation of celestial
mechanics. 2.3
Observations of Field-aligned Irregularities in
Meteor Trails Using the MU Radar
Qihou H. Zhou (1), Takuji Nakamura (2) and John
D. Mathews (3)
1) Arecibo Observatory, National Astronomy and
Ionosphere Center, Arecibo, Puerto Rico; 2) Radio
Science Center for Space and Atmosphere, Kyoto
University, Kyoto, Japan; 3) Communications and
Space Sciences Laboratory, Pennsylvania State
University, University Park, Pennsylvania
A large number of range-spread trail echoes
(RSTE) have been observed using the Kyoto
University Middle and Upper (MU) Atmosphere 46.5
MHz Radar. In fact, essentially all the head echoes
displaying an along-the-beam velocity component
were followed by range spread echoes in the
perpendicular-to-B pointing geometry. RSTE's are
typically observed a couple of hundred milliseconds
after the passage of the head echo. This indicates
the occurrence of plasma instability in meteor
trails. In addition, all the spectra are limited
within a bandwidth corresponding to a Doppler shift
of 320 m/s, suggesting that the two stream
instability is absent most of the time. The MU
observations show that the model of a smooth meteor
trail does not exist in reality. We will present
the characteristics of RSTE's and discuss the
implications of the MU observations on meteor
science and aeronomy applications. 7.3
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