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[Programme]
Session 5: "Impacts of Meteoroids on
the Atmosphere"
Date: Wednesday
8.30-10.00
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
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 - 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 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
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 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
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 - 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 - 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 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 'Äòin the
context of mainstream plasma physics'Äô.
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
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 - 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
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
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
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
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