Multi‐point observations of the inner boundary of the plasma sheet during geomagnetic disturbances

Abstract

We report on the THEMIS and Double Star TC‐1 observations at the geocentric distances of 3 < R < 8 RE during substorms on March 23, 2007. THEMIS crossed the inner boundary of the equatorial dusk‐side plasma in the string‐of‐pearls configuration, allowing the dynamics of particle populations to be traced within time ranges from hours to 10 minutes. Observations show co‐existence of the plasma sheet ion population (5 – 30 keV) with the ring current ion population (100 – 1000 keV) at 4 < R < 6 RE. The plasma sheet population was characterized by pronounced “nose”‐like dispersion with the spectral density maximum at ∼10 keV. The plasma sheet boundary, defined by a sharp decrease of the ∼1 keV electron flux, moved inward to R = 4 and outward back to ∼8 RE within about 1 hour. Local enhancements of the plasma sheet (1 – 5 keV) electron flux with the characteristic time scale of 2 – 10 min were detected at 5 < R < 6 RE during the substorm.