IRF Kiruna


Meteoroids 2001

Conference at the

Swedish Institute of Space Physics,

Kiruna, Sweden
6-10 August 2001


[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


[Programme]

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