N88- 14535
255
THE END HEIGHT OF FIREBALL AS A FUNCTION
OF THEIR RESIDUAL KINETIC ENERGY
D. 0. ReVelle
Meteorology Program
Northern Illinois University
DeKalb, Illinois, U.S.A.
Abstract
Previous analyses of meteoroid compositional groupings have
utilized the end height of fireballs as a diagnostic tool. From an
observational perspective this definition is straight forward, but from
a theoretical viewpoint there are problems with using this operational
definition. These include:
a) Dependence of end height on slant range due to extinction for
long optical paths;
b) Minimum mass sensitivity effects due to ablation, gross
fragmentation, etc.;
c) Limiting wavelength and amplitude detection due to sky
brightness, response of the emulsion, etc.;
d) Theoretical predictions of an optically thick radiation field
at low altitudes for high velocity entry (Biberman et al.,
1980).
In order to realistically assess the estimated geometric
uncertainty of + 1km in the observed end height, a theoretical
definition of the end height of meteoritic fireballs is proposed using
the results from the integral radiation efficiency model of REVELLE
(1980). Three photographed and recovered meteorites, Pribram, Lost City
and Innisfree are used as a calibration for this proposed definition.
These three fireballs were calculated as having about 99% of their
pre-atmospheric kinetic energy removed prior to the dark flight phase.
Assuming that a fixed fraction of the initial kinetic energy will remain
at the end height, a prediction of the theoretical end height can be
made directly.
This definition has been used to evaluate the end height of all
fireballs that were deduced by WETHERILL and REVELLE (1981) as being
"meteoritic". In almost all cases the theoretical values are lower than
the observed values, in some cases being as much as 5km lower. A
preliminary summary table of results is given below.
This work was supported by Universities Space Research Association
while the author was a Visiting Scientist at NASA/MSFC, Huntsville,
Alabama.
Evaluation of fireball end heights with 0 = 0.02 /km , H = 8 km and D = 4.60.
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POOR QUAUTy
257
REFERENCES
1. L.M. Biberman, C. Ya. Bronin and M.V. Brykin: Motion of a Blunt
Body Through the Dense Atmosphere Under Conditions of Severe
Aerodynamic Heating and Ablation, Acta Astronautica , 7, 53-65,
1980.
2. D.O. ReVelle: A Predictive Macroscopic Integral Radiation
Efficiency Model, J. Geophys. Res. , 85, 1803-8, 1980.
3. G.W. Wetherill and D.O. ReVelle: Which Fireballs are Meteorites?,
A Study of the Prairie Network Photographic Meteor Data, Icarus ,
48, 308-28, 1981.
4. D. 0. ReVelle: A Quasi-Simple Ablation Model for Large Meteorite
Entry: Theory Versus Observations, Journal of Atmospheric and
Terrestrial Physics , 41 , 453-73, 1979.
