Coordinated observation of the dayside magnetospheric entry and exit of the THEMIS satellites with ground‐based auroral imaging in Antarctica

Abstract

Data from the five‐satellite Time History of Events and Macroscale Interactions during Substorms (THEMIS) constellation suitably located to study solar wind magnetospheric coupling during the austral winter of 2007 were compared to data from ground‐based all‐sky imagers (ASIs) at South Pole (74° magnetic latitude) and at AGO‐1 (80° magnetic latitude). The THEMIS constellation entered and exited the magnetosphere near magnetic midday on 10 and 12 August 2007, respectively. On 12 August interplanetary magnetic field (IMF) (Bz > 0) the dayside aurora was located more poleward between AGO‐1 and South Pole. The THEMIS satellites traversing the magnetopause saw it move in and out several times during the satellite crossings. The inward motion of the magnetopause was sometimes correlated with equatorward expansions of the aurora and sometimes with solar wind pressure pulses as seen by Geotail. The Bz > 0 auroral latitude was consistent with dayside cusp “spot” seen by the IMAGE spacecraft and had been associated with footprints of “steady state” lobe reconnection. The aurora consisted of a continuous stream of poleward moving auroral forms (PMAF) even during a period of slightly Bz > 0 and By = 0. On 10 August 2007 IMF Bz < 0 the dayside aurora was located more equatorward, over South Pole, and the THEMIS satellites crossed the bow shock from the magnetosheath into the solar wind. Negative Bz pulses observed at the satellite were correlated with large poleward expansions of the dayside aurora consistent with reconnection in the subsolar region accompanied by simultaneous plasma density increases at THEMIS B satellite consistent with outward radial motion of the bow shock.