Temperature anisotropies in the terrestrial ionosphere and plasmasphere

Theoretical work in which the solution of closed sets of transport equations has predicted the existence of temperature anisotropies in the terrestrial ionosphere-plasmasphere system is discussed, considering only thermal (less than 1 eV) particle populations. Various models used to predict ion and electron temperature anisotropies, including kinetic, semikinetic, hydromagnetic, and generalized transport models, predict temperature anisotropies in the polar wind, along plasmapause field lines, during the refilling of the outer plasmasphere after depletion by a magnetic storm, and at F region altitudes in regions of rapid plasma convection. However, only some of the theoretical predictions agree with experimental evidence. Other models predict isotropic temperature distributions in regions where observations indicated the presence of temperature anisotropies.