PC index as a proxy of the solar wind energy that entered into the magnetosphere: 2. Relation to the interplanetary electric field E KL before substorm onset

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• 作者：OA Troshichev ; DA Sormakov
• 关键词：Interplanetary electric field E KL ; PC index ; Magnetic substorms ; Delay time ; Solar wind parameters growth rate ; Solar wind energy input
• 刊名：Earth, Planets and Space
• 出版年：2015
• 出版时间：December 2015
• 年：2015
• 卷：67
• 期：1
• 全文大小：1,891 KB
• 刊物类别：Earth Sciences, general; Geology; Geophysics/Geodesy;
• 刊物主题：Earth Sciences, general; Geology; Geophysics/Geodesy;
• 出版者：Springer Berlin Heidelberg
• ISSN：1880-5981

文摘

This paper (the second of a series) presents the results of statistical investigation of relationship between the interplanetary electric field E _KL and the Polar Cap (PC) index in case of magnetic substorms (1998–2001), which have been analyzed in Troshichev et al. (J. Geophys. Res. Space Physics, 119, 2014). The PC index is directly related to the E _KL field variations on interval preceding the substorm sudden onset (SO): correlation R > 0.5 is typical of more than 90 % of isolated substorms, 80 % of expanded substorms, and 99 % of events with coordinated E _KL and PC jumps. The low or negative correlation observing in ~10 % of examined substorms suggests that the solar wind flow measured by the Advanced Composition Explorer (ACE) spacecraft in the Lagrange point L1 did not encounter the magnetosphere in these cases. Examination of the delay times ΔT in the response of PC index to E _KL variations provides the following results: (1) delay times do not depend on separate solar wind parameters, such as solar wind speed V _X and interplanetary magnetic field (IMF) B _Z component, contrary to general conviction, (2) the ΔT value is best controlled by the E _KL field growth rate (dE _KL/dt), (3) the lower ΔT limit (5–7 min is attained under conditions of the higher E _KL growth rate, and (4) the PC index provides the possibility to verify the solar wind flow transportation time from ACE position (where the solar wind speed is estimated) to magnetosphere. These results, in combination with data testifying that the substorm onsets are related to the PC precursors, demonstrate that the PC index is an adequate ground-based indicator of the solar wind energy incoming into the magnetosphere.