Temperature anisotropies in the terrestrial ionosphere and plasmasphere

摘要

The available theoretical and experimental evidence for ion and electron temperature anisotropies in the terrestrial ionosphere‐plasmasphere system is reviewed. The review is concerned only with temperature anisotropies in the thermal (less than 1 eV) populations and does not cover energized auroral populations, such as ion beams, conics, and bowl distributions. Currently, the bulk of the work dealing with temperature anisotropies has been theoretical. Various models have been used to predict ion and electron temperature anisotropies, including kinetic, semikinetic, hydromagnetic and generalized transport models. Temperature anisotropies have been predicted in the polar wind, along plasmapause field lines, during the refilling of the outer plasmasphere after depletion by a magnetic storm, and atFregion altitudes in regions of rapid plasma convection. The experimental evidence for temperature anisotropies, on the other hand, is limited. Some of the observations support the theoretical predictions, while other observations indicate the presence of temperature anisotropies in regions where the models predict isotropic temperature distributions. More extensive observations are needed in order to elucidate the underlying processes controlling the thermal structure in the ionosphere‐plasmasphere sys