Successive Dipolarization Fronts With a Stepwise Electron Acceleration During a Substorm in Saturn's Magnetotail

Abstract

AbstractSubstorms are a fundamental phenomenon in planetary magnetospheric systems. Using Cassini measurements, we report a typical event in which four successive dipolarization fronts (DFs) were observed within 1 hour during the substorm in Saturn's magnetotail. The last three DFs caused a type of stepwise electron acceleration and generated energetic electrons. The pitch angle distributions of the electrons show evidence of the Fermi acceleration mechanism behind these DFs. Therefore, we infer the magnetotail dynamics process during Saturn's substorm: The stepwise acceleration by successive DFs powerfully accelerates the field‐aligned electrons and generates field‐aligned energetic electrons. These high‐energy electrons are injected into the inner magnetosphere and become an important trigger of Saturn's aurora. Our results show an efficient acceleration mechanism for the electrons caused by successive DFs and confirm an important source of energetic particles during the substorm in Saturn, and these findings improve our understanding of Saturn's substorm and magnetotail dynamics.