Interplanetary Magnetic Field Control of Polar Ionospheric Equivalent Current System Modes
Interplanetary Magnetic Field Control of Polar Ionospheric Equivalent Current System Modes
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DOI：
10.1029/2019sw002161
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发表时间：
2019-07
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影响因子：
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通讯作者：
R. Shore;M. Freeman;Jesper Gjerloev
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文献类型：
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作者：
R. Shore;M. Freeman;Jesper Gjerloev
分析了不同电离层等效电流模式对行星际磁场（IMF）分量By和Bz变化的响应。每个模态都包含一个固定的空间模式，其振幅随时间变化，通过逐月的表面测量磁场方差的经验正交函数分离来识别。在这里，我们将重点讨论四组模式，它们分别是DPY、DP2、NBZ和DP1。我们推导了相对于弓形激波机头的IMF状态，在- 10到+600分钟的滞后范围内，每个模式与IMF By或Bz设置的相互关联函数。对于所有四组模式，平均相关性可以通过对IMF分量的最多三个线性响应的总和来再现，每个线性响应都以不同的滞后为中心。这些被解释为电离层对磁层顶合并（15 - 20分钟延迟）和磁尾重联（60分钟延迟）以及IMF持续性的统计响应。在模式集中，NBZ和DPY从给定的IMF分量是最可预测的，而DP1（次风暴分量）是最不可预测的。国际货币基金组织解释的模式变率比例随着滞后时间的延长而增加，这被认为表明了亚暴的电导率反馈。总之，我们确认了这些模式的假设物理基础，并量化了它们的多重重构时间尺度。
We analyze the response of different ionospheric equivalent current modes to variations in the interplanetary magnetic field (IMF) components By and Bz. Each mode comprises a fixed spatial pattern whose amplitude varies in time, identified by a month‐by‐month empirical orthogonal function separation of surface measured magnetic field variance. Here we focus on four sets of modes that have been previously identified as DPY, DP2, NBZ, and DP1. We derive the cross‐correlation function of each mode set with either IMF By or Bz for lags ranging from −10 to +600 mins with respect to the IMF state at the bow shock nose. For all four sets of modes, the average correlation can be reproduced by a sum of up to three linear responses to the IMF component, each centered on a different lag. These are interpreted as the statistical ionospheric responses to magnetopause merging (15‐ to 20‐min lag) and magnetotail reconnection (60‐min lag) and to IMF persistence. Of the mode sets, NBZ and DPY are the most predictable from a given IMF component, with DP1 (the substorm component) the least predictable. The proportion of mode variability explained by the IMF increases for the longer lags, thought to indicate conductivity feedbacks from substorms. In summary, we confirm the postulated physical basis of these modes and quantify their multiple reconfiguration timescales.