Two types of PSBL ion beam observed by Geotail: Their relation to low frequency electromagnetic waves and cold ion energization

Two types of the plasma sheet boundary layer (PSBL) crossing during a geomagnetically active period are analyzed in detail to investigate relationship between the ion beams, low-frequency (0.01-2 Hz) electromagnetic waves, and cold ion energization in PSBL using the Geotail data. In response to changes in the solar wind conditions and auroral activity inferred from the AL index, the properties of PSBL ions changed dramatically: During the less disturbed period, we observed counter-streaming thermalized beams with no significant wave activity in the low-frequency range. The thermalized beams may be generated from the distant magnetotail and have undergone thermalization before reaching the Geotail position of X ∼ −30RE. During the periods of enhanced auroral activity with southward IMF, collimated freshly injected earthward beams are observed together with the large-amplitude electromagnetic waves having a peak around 0.025 Hz (∼0.1Ωci). Cold ions are energized during the periods of large-amplitude low-frequency fluctuations. It is suggested that fresh beams from the near-Earth neutral line (NENL) play an important role in the cold ion energization.