Observation evidence for the entropy switch model of substorm onset

作     者：YunXiang Song ChuXin Chen YunXiang Song;ChuXin Chen

作者机构：CAS Key Laboratory of Geospace EnvironmentDepartment of Geophysics and Planetary SciencesSchool of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China 

出 版 物：《Earth and Planetary Physics》 (地球与行星物理（英文版）)

年 卷 期：2022年第6卷第2期

页      面：161-176页

核心收录：

学科分类：070802[理学-空间物理学] 07[理学] 0708[理学-地球物理学] 

基　　金：supported by the National Natural Science Foundation of China(Grant No.NSFC41974204) 

主　　题：substorm onset entropy switch model interchange or ballooning instability Time History of Events and Macroscale Interactions during Substorms(THEMIS)data 

摘      要：The cause of substorm onset is not yet understood. Chen CX(2016) proposed an entropy switch model, in which substorm onset results from the development of interchange instability. In this study, we sought observational evidence for this model by using Time History of Events and Macroscale Interactions during Substorms(THEMIS) data. We examined two events, one with and the other without a streamer before substorm onset. In contrast to the stable magnetosphere, where the total magnetic field strength is a decreasing function and entropy is an increasing function of the downtail distance, in both events the total magnetic field strength and entropy were reversed before substorm onset. After onset, the total magnetic field strength, entropy, and other plasma quantities fluctuated. In addition, a statistical study was performed. By confining the events with THEMIS satellites located in the downtail region between ~8 and ~12 Earth radii, and 3 hours before and after midnight, we found the occurrence rate of the total magnetic field strength reversal to be 69% and the occurrence rate of entropy reversal to be 77% of the total 205 events.