Spatial distributions of ion pitch angle anisotropy in the near-Earth magnetosphere and tail plasma sheet

摘要: [1] We have quantified anisotropy of ion pitch angle distributions observed by the Time History Events and Macroscale Interactions during Substorms (THEMIS) spacecraft determined statistically how varies with particle energy, as well spatial dependences on geomagnetic activity. In tail plasma sheet, ions from a few keV to tens are mostly isotropic. The locations energy ranges for these isotropic their changes Dst consistent being isotropized current sheet scattering predicted using empirical magnetic field models. Ions hundreds in cigar-shaped or unidirectional distribution (PAD) likely result Speiser motion. majority near-Earth magnetosphere expected conserve first second adiabatic invariants they move dependent drift. This gives drift shell splitting, which plays an important role generating pancake-shaped PAD ~1 keV up keV. local time pancake rotates increasing energy. Loss near 90° due magnetopause shadowing can further explain butterfly-shaped at postmidnight sector energies above 30 keV. For below eV magnetosphere, is dominantly bidirectional, ionosphere outflow. High-energy dayside become less anisotropic higher AE, when electromagnetic cyclotron waves may play role.