Multipoint observations of compressional Pc5-6 pulsations in the dawn side magnetosphere: A case study

Abstract

We present a case study of compressional Pc5-6 pulsations observed by THEMIS-D and -E in the dawn sector of the magnetosphere following 1100 UT on January 22, 2010. The pulsations were observed during a moderate substorm triggered by the IMF discontinuity and an accompanying change in the solar wind dynamic pressure at 1045 UT. The event can be considered a stormtime Pc5-6 event. We determine the characteristics of the waves, including their velocity, azimuthal wave number m and wavelength. The arrival of particles injected by the substorm caused favorable conditions for the development of the mirror-mode instability and therefore initiated the pulsations. A decrease in the solar wind density and dynamic pressure at 1250 UT was seen in the dayside magnetosheath, corresponding to diminished dayside magnetospheric magnetic fields strengths and terminated the compressional Pc5-6 pulsations. We deduce that the pulsations observed by THEMIS might be internally initiated and externally terminated.