Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsa21b1448z&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SA21B-1448
Other
[0355] Atmospheric Composition And Structure / Thermosphere: Composition And Chemistry, [2459] Ionosphere / Planetary Ionospheres, [3360] Atmospheric Processes / Remote Sensing, [6015] Planetary Sciences: Comets And Small Bodies / Dust
Scientific paper
We describe a new analysis of a set of 32 meteor radar traces recorded with the 430 MHz Altair radar facility in November 1998. We find that in most of the cases the measured velocity vs altitude data can be fitted quite accurately as quadratic functions of the path-integrated atmospheric column densities, and the decelerations derived from those fits show the expected behavior of increasing with decreasing altitude. From the deceleration vs altitude fits in each case we determine a best-fit value for the effective average ablation coefficient. From a computer model that integrates the equations for meteor velocity, temperature and mass vs altitude we conclude, in agreement with other authors, that the ablation rates are controlled primarily by the rates of evaporation of individual meteor constituents from a molten meteor. We also compute the steady-state meteor temperatures consistent with the equilibria between the rates of heating by air molecule collisions and cooling by blackbody emission and by evaporation. At each altitude the equilibrium temperature is a function of the local air density and meteor velocity, together with the meteor constituent thermodynamic properties, but is independent of the meteor mass and mass density. From the steady-state temperatures and constituent properties we can compute the evaporation rates and evaluate the effective local values of the ablation coefficients. We find that, for any specified meteor constituent, as the altitudes decrease the effective ablation coefficients for different meteor velocities all tend to converge to the same asymptotic value, which is equal to 0.5 times the vapor molecular mass divided by the heat of sublimation. This is related to the fact that at the lowest altitudes the meteor cooling rates are dominated by evaporative cooling rather than blackbody emission. We also present results from the detailed computer model that integrates the ordinary differential equations for the meteor masses, velocities and temperatures as functions of altitude and time -- for meteors with one or several mineral constituents.
Close Sigrid
Colestock Patrick L.
Loveland Rohan
MacDonell A.
Zinn Joel
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