Conjugate observation of auroral finger‐like structures by ground‐based all‐sky cameras and THEMIS satellites

Abstract

AbstractIn this study, we analyze the first conjugate observation of auroral finger‐like structures using ground‐based all‐sky cameras and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites and investigated associated physical processes that are a cause of auroral fragmentation into patches. Two events are reported: one is a conjugate event, and the other is a nearly conjugate event. The conjugate event was observed at Narsarsuaq (magnetic latitude: 65.3°N), Greenland, at 0720–0820 UT (0506–0606 LT) on 17 February 2012. Analysis of the event revealed the following observational facts: (1) variation of parallel electron energy fluxes observed by THEMIS‐E shows a correspondence to the auroral intensity variation, (2) plasma pressure and magnetic pressure fluctuate in antiphase with time scales of 5–20 min, and (3) perpendicular ion velocity is very small (less than 50 km/s). In the latter event, observed at Gakona, Alaska, on 2 February 2008, the THEMIS‐D satellite passed across higher latitudes of finger‐like structures. The data from THEMIS‐D also showed the antiphase fluctuation between plasma pressure and magnetic pressure and the small perpendicular ion velocity. From these observations, we suggest that the finger‐like structures are caused by a pressure‐driven instability in the balance of plasma and magnetic pressures in the magnetosphere.