Investigating Rotation and Anisotropic Ablation of Small Meteoroids and Their Effects on Head Echo Plasma Formation via Computational Techniques

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.