Observations of the warm plasma cloak and an explanation of its formation in the magnetosphere

Previous studies of the magnetospheric plasma populations have concentrated on the low‐energy (1 eV) plasma of the plasmasphere, the more energetic (1‐100 keV) plasma of the plasma sheet and ring current, and the high‐energy (approximately MeV) plasma of the radiation belts. A compilation of satellite measurements over the past 30 years augmented by recent observations from the Polar‐TIDE instrument has revealed a new perspective on a plasma population in the middle magnetosphere. This population consists of ions with energies of a few eV to greater than several hundred eV which display a characteristic bidirectional field‐aligned pitch angle distribution. Measurements from the ATS, ISEE, SCATHA, DE, and POLAR satellites establish the characteristics of this “warm plasma cloak” of particles that is draped over the nightside region of the plasmasphere and is blown into the morning and early afternoon dayside sector by the sunward convective wind in the magnetosphere. The satellite observations combined with the predictions of an ion trajectory model are used to describe the formation and dynamics of the warm plasma cloak.