Ion Cyclotron Waves Rippling Ballooning/InterChange Instability Heads

A dawnward drifting Ballooning/InterChange Instability (BICI) head is identified and studied using high‐resolution Time History of Events and Macroscale Interactions during Substorms observations at XGSM≈−11RE on 15 February 2008 between 10:18 UT and 10:30 UT and compared with particle‐in‐cell simulation run results for a charged current sheet. A prediction of the earlier particle‐in‐cell simulation for a neutral sheet, that duskward drifting BICI heads are subject to a current‐driven ion cyclotron instability, is found to be true also for dawnward drifting BICI heads in the charged sheet simulations. This specific prediction and the Time History of Events and Macroscale Interactions during Substorms data indicate the presence of electromagnetic ion cyclotron wave activity that ripples the background BICI head shape. The waves propagated azimuthally with δEy/δBz≈4.5VA. The waves are found in a region of the strongest differential drift between the electrons and ions, suggesting that the drift generated the waves. Key Points High‐frequency THEMIS data of a BICI head crossing are compared with PIC simulations Electromagnetic ion cyclotron instability waves rippled the head Differential drift between the electrons and ions drives the instability