Two Successive Interplanetary Shock-induced Plasmaspheric Hiss Variability: Disappearance, Reappearance and Patchiness

Abstract:

Plasmaspheric hiss is an extremely low frequency electromagnetic emission confined inside the plasmasphere and duskside plasmaspheric plumes. Statistically, such waves are found to enhance during intense geomagnetic intervals but reports of its disappearance following interplanetary shocks are also now available in literature. Thus, the mechanisms behind its generation and variability in response to external perturbations are still subjects of ongoing research. In the present case, we observed a complex response of plasmaspheric hiss to two successive shock impacts. On December 19, 2015, two interplanetary shocks impinged on the magnetosphere within an interval of ~2 hours. From Van Allen Probes observations, we noticed disappearance of hiss with the arrival of the first shock which recovered after almost 45 minutes. Following the second shock, intermittent hiss were generated lasting for about an hour after which the wave regained its ambient intensity. This is a first direct observational evidence of plasmaspheric hiss variability following two successive shock impacts. The plausible explanations for the observed hiss variabilities will be presented in details in this study.