Visualization of ion cyclotron wave and particle interactions in the inner magnetosphere via THEMIS‐ASI observations

Abstract

Interaction with EMIC (electromagnetic ion cyclotron) waves is thought to be a key component contributing to the very rapid loss of both ring current and radiation belt particles into the atmosphere. Estimated loss rates are heavily dependent on the assumed spatial distribution of the EMIC wave. Statistical maps of the spatial distribution have been produced using in‐situ satellite data. However, with limited satellite data it is impossible to deduce the true spatial distribution. In this study, we present ground‐based observations using all‐sky imager and search coil magnetometer networks, which provide the large‐scale distribution and motion of the EMIC wave‐particle interaction regions. We observed several spots of isolated proton auroras simultaneously with Pc1/EMIC waves at subauroral latitudes during the expansion phase of a storm‐time substorm on 9 March 2008. The isolated auroras were distributed over ∼4‐hours MLT preceding midnight. The POES‐17 satellite confirmed enhancements of 30‐keV proton precipitations over the isolated auroras. The equatorward motion of the auroras and frequency drift of the wave were consistent with the plasmasphere eroding due to a polar cap potential enhancement modeled by a numerical simulation. We also found that relativistic electron precipitation was not always associated with the isolated aurora, depending strongly on the plasma density profile near the plasmapause. This study shows that the specific distribution of ring current proton precipitation can be visualized through the ground network observations. By combining with upcoming inner‐magnetosphere satellite missions, these remote‐sensing observations are very important for quantitative understanding of the particle loss in the inner magnetosphere.