Evidence of H+‐Band EMIC Waves in the Inner Radiation Belt Observed by Van Allen Probes During Magnetic Storms

Abstract

AbstractElectromagnetic ion cyclotron (EMIC) waves play an important role in the losses of ring current ions and outer radiation belt relativistic electrons. While EMIC waves have been reported to occur frequently in the outer belt and slot region, there is little information about the occurrence of EMIC waves in the inner radiation belt. On basis of the magnetometer observations from Van Allen Probes, we analyze two representative events of H+‐band EMIC waves that occurred in the inner zone on December 21 and June 22, 2015. We find that these waves occurred synchronously accompanying with 5–35 keV proton dispersive injections at the dawn and night sectors. During the periods of EMIC waves, the perpendicular temperature of injected protons increased, while the corresponding parallel component decreased. By analyzing the relation between the temperature anisotropy and parallel plasma beta for the two cases, we suggest that the evident enhancements of the temperature anisotropy (T⊥/T∥) of 5–35 keV protons may provide the energy source to excite the H+‐band EMIC waves. A total of 16 left‐hand H+‐band EMIC wave events have been found in the inner radiation belt during the 4‐year (2013–2016) interval and all occur during magnetic storms. The statistical results implicated that left‐hand H+‐band EMIC waves in the inner radiation belt is associated with storm‐time ion injections.