Plasma Anisotropies and Currents in the Near-Earth Plasma Sheet and Inner Magnetosphere

摘要

The region occupying radial distances of ~3-9 Earth radii (R_E) in the nightside includes the near-Earth plasma sheet with stretched magnetic field lines and the inner magnetosphere with strong dipolar magnetic field. In this region, the plasma flow energy, which was injected into the inner magnetosphere from the magnetotail, is converted to particle heating and electromagnetic wave generation. These important processes are controlled by plasma anisotropies, which are the focus of this study. Using measurements of Time History of Events and Macroscale Interactions during Substorms and Van Allen Probes in this transition region we obtain radial profiles of ion and electron temperatures and anisotropies for various geomagnetic activity levels. Ion and electron anisotropies vary with the geomagnetic activity in opposite directions. Parallel anisotropic ions are observed together with transversely anisotropic electrons, whereas the change of ion anisotropy from parallel to transverse (with increasing K_p) is accompanied by the electron anisotropy changing from transverse to parallel. Based on plasma anisotropy observations, we estimate that the anisotropy-related currents (curvature currents) are about 10-20% of the diamagnetic currents.