Description of space plasmas exhibiting temperature anisotropies for subsonic flow

This paper compares solutions to the bi-Maxwellian based 16-moment transport equations with those obtained from the Maxwellian-based 13-moment transport equations for conditions leading to steady-state, subsonic flow of a fully-ionized electron-proton plasma along geomagnetic-field lines. An in-depth review of past work in the field of ionospheric temperature anisotropies, covering both theoretical models and experimental observations, was presented first in order to provide a background for and clarify the meaning of the original research to follow. Both the 16 and 13-moment sets were expressed in a dipolar coordinate system and numerically integrated along the direction of the geomagnetic field. The comparison was conducted for a range of lower boundary temperatures (2000-10,000 K) and temperature gradients (1-4 K km-1) over the altitude range from 1500-13,000 km. These boundary parameters are the most important in the subsonic flow regime since they produce different temperature anisotropies and heat flows, which are handled differently in the two formulations. The 16-moment set, based on a zeroth-order bi-Maxwellian (two-temperature) velocity distribution function, can account for large temperature anisotropies and the flow of both parallel and perpendicular thermal energy, while the 13-moment set, based on a zeroth-order distribution that is Maxwellian (temperature isotropic), can account for small temperature anisotropies and only a total heat flow