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Abstract High‐power large‐aperture radar instruments observe numerous meteor head echoes per minute. Head echoes result from reflections of radio waves from plasma surrounding meteoroids as they enter Earth's atmosphere. Knowledge of the spatial distribution of electrons in this plasma is essential to determining the mass loss rate of the meteor as a function of its measured radar cross‐section. Prior work applies theoretical and computational methods to determine the electron density distribution, but assumes the meteoroid emits neutral particles uniformly across its surface. In this paper, a numerical surface ablation model demonstrates that meteoroid mass loss may occur preferentially in the direction facing the oncoming atmosphere. Specifically, meteoroid mass loss becomes proportional to the frontal surface area facing the freestream atmosphere in the limit of high Biot number, but remains isotropic in the limit of low Biot number. Meteoroid rotation has a small effect on the direction of ejected mass, but the effect is insignificant compared to variation in meteoroid properties that affect the Biot number. This result informs our computational meteor plasma model, in which we compare the effect of meteoroid vaporization on the plasma distribution in the limits of low versus high Biot number. The resulting electron density profiles demonstrate order‐of‐magnitude agreement between each other, with peak difference of 70% immediately upstream of the meteoroid. This implies that the directional distribution of vaporizing neutrals likely does not significantly influence head echo observations, lending credence to existing work that assumes isotropic ablation. 

This paper develops a unified linear theory of cross field plasma instabilities, including the Farley–Buneman, electron thermal, and ion thermal instabilities, in spatially uniform collisional plasmas with partially unmagnetized multi-species ions. Collisional plasma instabilities in weakly ionized, highly dissipative, weakly magnetized plasmas play an important role in the lower Earth's ionosphere and may be of importance in other planetary ionospheres, stellar atmospheres, cometary tails, molecular clouds, accretion disks, etc. In the Earth's ionosphere, these collisional plasma instabilities cause intense electron heating. In the solar chromosphere, they can do the same—an effect originally suggested from spectroscopic observations and modeling. Based on a simplified 5-moment multi-fluid model, the theoretical analysis presented in this paper produces the linear dispersion relation for the combined Thermal Farley–Buneman Instability with an important long-wavelength limit analyzed in detail. This limit provides an easy interpretation of different instability drivers and wave dissipation. This analysis of instability, combined with simulations, will enable us to better understand plasma waves and turbulence in these commonly occurring collisional space plasmas.