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[Programme]
Session 3: "Physics and Chemistry of
Meteors"
Date: Tuesday 8.30-11.20
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
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
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
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
About Pulsation Brightness of the Bright
Meteors
G. G. Novikov and O.V. Sokolov
On the example of the solutionof 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 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
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 -- Lyrids,
eta-Aquarids, Perseid, Orionids, Leonids, Geminids
as well as many sporadic meteors -- 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
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
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
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