THEMIS Observations of Plasma Sheet Region 1 and 2 Birkeland Currents in Quiet and Substorm Times
Thursday, 26 May 2016
Jiang Liu1, Vassilis Angelopoulos2, Xiangning Chu1 and Andrei Runov1, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)University of California Los Angeles, Earth, Planetary, and Space Sciences, Los Angeles, CA, United States
Abstract:
Although region 1 and 2 Birkeland currents are closely related to geomagnetic activities such as substorm initiation, their magnetospheric origin remains not well known. We look for the origin of nightside Birkeland currents using multi-point observations from THEMIS in the 8-12 RE downtail region. Our statistical study reveals that region 1 and 2 currents exist in the plasma sheet at both quiet and active times. The region 2 current is buried deep inside the plasma sheet (this is found for the first time), whereas the region 1 current is farther away from the neutral sheet, extending to the plasma sheet boundary layer. At geomagnetic quiet times, the separation layer between the region 2 and 1 currents is located at ~2.5 RE from the neutral sheet. During substorms, the separation layer migrates towards (away from) the neutral sheet when the plasma sheet thins (thickens). These findings suggest that the plasma sheet is a source of region-1 and -2 Birkeland currents regardless of geomagnetic activity level, and its evolution controls the distribution of FACs in the magnetotail.
