Small-scale filamentary structures recorded in the auroral regions connected to the plasma sheet boundary layer

Abstract

[1] We use high time resolution data from the FAST spacecraft during a moderate substorm and concentrate on the auroral regions that are magnetically linked to the plasma sheet boundary layer (PSBL). The crossing of these regions is characterized by the presence of a pair of oppositely directed, field-aligned current sheets. The more poleward of the two current sheets is directed earthward. Strong turbulent fluctuations are detected in association with the field-aligned currents. The low-frequency component (∼1 Hz) of the electric field fluctuations consists of localized structures whose characteristics are not entirely consistent with the presence of Alfven waves. They may represent a possible example of the coupling of Alfven waves with electron acoustic waves on small length scales. In the high-frequency range (∼1–10 kHz), the turbulent fluctuations are dominated by large amplitude (∼500 mV/m peak to peak) bipolar electric field structures whose polarity depends on the direction of the field-aligned currents. These latter structures are moving earthward in the upward current region and antiearthward in the downward current region. The generation of both low- and high-frequency filamentary nonlinear structures appears as a natural consequence of the disturbances imposed during substorms on the auroral regions connected to the PSBL when hot and cold plasmas interact.