Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa31b..05d&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SA31B-05
Physics
6245 Meteors, 0654 Plasmas, 2411 Electric Fields (2712), 2435 Ionospheric Disturbances, 2442 Meteor-Trail Physics
Scientific paper
A meteoroid penetrating the Earth's atmosphere leaves behind a trail of dense plasma in the E-region ionosphere, a region where electrons are strongly magnetized while ions are demagnetized due to their frequent collisions with neutrals. While radar measurements of meteor trail evolution have been collected and used to infer meteor and atmospheric properties since the 1950s, no accurate quantitative model of trail fields and diffusion exists. We have developed analytical theory and simulations of trail plasma physics which applies to the majority of small meteors and can accurately model trail evolution for trails at a broad range of altitudes and initial plasma densities. This study provides quantitative knowledge of the spatial distribution and dynamics of the plasma density and electric field. Structure of plasma density is important for specular radar echoes. The ambipolar electric field can drive plasma instabilities resulting in non-specular radar echoes. Both simulations and theory show that at altitudes above 94km, meteor trails initially become highly anisotropic due to the different diffusion rates for electrons and ions. With time, however, the trail diffusion becomes nearly isotropic due to its interaction with the background plasma. The transition from anisotropic to isotropic diffusion takes place when the plasma trail density remains much larger than the background plasma. This may help explain unexpected results of some radar observations of specular echoes. Ambipolar diffusion of trails leads gives rise to polarization electric fields, which may drive plasma instabilities and generate electron density irregularities visible to radars as non-specular echoes. During the trail evolution, when the trail diffusion becomes more isotropic, the electric field may drop below the level necessary to drive instabilities. This is of importance for interpretation of non-specular trails.
Dimant Ya. S.
Oppemheim M. M.
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