Spacecraft Potential Changes Associated With EMIC Waves in the Inner Magnetosphere

Abstract

Although electromagnetic ion cyclotron (EMIC) waves are commonly observed in the magnetosphere and are believed to energize background cold ions, it is not clear whether EMIC waves play a significant role in determining spacecraft potential change. In this paper, we present two strong He-band EMIC wave events observed by the Van Allen Probe-B spacecraft inside the plasmasphere. One event occurred on 11 March 2016 when the spacecraft was on the dayside, and the other occurred on 9 October 2016 when the spacecraft was in the postmidnight sector. When a strong He-band EMIC wave activity was detected, low-energy ion flux enhancements occurred nearly simultaneously with the EMIC wave power enhancements. Both events presented in this study are clearly unique in that He-band wave power and enhanced proton flux are extremely high. During the wave activity interval, we found that the spacecraft charged more positively without a significant change in the ambient electron density. We discuss whether low-energy ions energized by EMIC waves can contribute to the spacecraft potential change.