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Observation evidence for the entropy switch model of substorm onset

Earth and Planetary Physics 2022年第2期6卷 161-176页

作者： YunXiang Song ChuXin Chen CAS Key Laboratory of Geospace Environment Department of Geophysics and Planetary SciencesSchool of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China

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.

关键词： substorm onset entropy switch model interchange or ballooning instability Time History of Events and Macroscale Interactions during substorms(THEMIS)data

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The substorm current wedge and midnight sector partial ring current near substorm onset: A synthesis based on a magnetotail magnetic field geometry model

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Advances in Polar Science 2013年第1期24卷 32-41页

作者： George J Sofko Kathryn A McWilliams Chad R Bryant Institute of Space & Atmospheric Studies University of Saskatchewan

The substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-pa

关键词： magnetotail magnetic field model auroral substorm substorm current wedge partial ring current substorm onset

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The Near-Earth BBFs and Its Relationship with AE Index

The Near-Earth BBFs and Its Relationship with AE Index

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第十二届全国日地空间物理学术讨论会

作者： W.Baumjohann Space Research Institute Austrian Academy of SciencesGrazAustria

We statistical analyzed the earthward high-speed flow in the near-Earth region explored by TC-1. From June 1,2004 to October 31,2006,a total 94 convective flow burst events are observed by the TC-1 satellite in the ne... 详细信息

关键词： BBF near-Earth AE index substorm onset

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