Solar wind control of plasma number density in the near-earth plasma sheet
Solar wind control of plasma number density in the near-earth plasma sheet
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DOI：
10.1029/2007ja012284
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发表时间：
2007-09
影响因子：
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通讯作者：
D. Nagata;S. Machida;S. Ohtani;Y. Saito;T. Mukai
中科院分区：
文献类型：
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作者：
D. Nagata;S. Machida;S. Ohtani;Y. Saito;T. Mukai
[1]等离子体片中的等离子体数密度依赖于太阳风数密度和行星际磁场的南北分量（IMF Bz），并有几个小时的时滞。通过将等离子体片和太阳风的观测结果拟合到经验模型方程中，我们研究了近地等离子体片中（X，Y）坐标的函数关系。通过优化拟合的相关系数，我们探索了IMF Bz的最短和最长响应时滞。分别对IMF向北和向南的主导条件进行了分析。在向南的IMF主导条件下，等离子体片数密度对太阳风数密度的依赖性在近尾区（r > 20 RE）较强。在南向IMF主导条件下，这种依赖性具有弱的晨昏不对称性，而在北向IMF主导条件下，这种依赖性在黄昏侧较强。在北向IMF主导条件下，全球范围内对IMF Bz的依赖性为正，而在南向IMF主导条件下，近地午夜前区域对IMF Bz的依赖性为负。最短和最长的时间滞后增加从中尾到近地球午夜前的区域向南IMF的优势条件。另一方面，最短（最长）的时间滞后增加逆向阳（向阳）沿着侧翼在北IMF优势条件。这些功能可以解释在重联和Kelvin-Helmholtz扩散机制的磁鞘等离子体进入等离子体片和等离子体片中的电和磁漂移传输。
[1] The plasma number density in the plasma sheet depends on the solar wind number density and the north-south component of interplanetary magnetic field (IMF Bz) with the time lag of several hours. We examined such dependences as functions of (X, Y) coordinates in the near-Earth plasma sheet by fitting observations of plasma sheet and solar wind to an empirical model equation. We explored shortest and longest response time lags to IMF Bz by optimizing the correlation coefficient of fit. Analyses were conducted separately for northward and southward IMF dominant conditions. The dependence of plasma sheet number density on solar wind number density is stronger in the near-tail region (r > 20 RE) under the southward IMF dominant condition. The dependence has weak dawn-dusk asymmetry under the southward IMF dominant condition, whereas it is stronger in the dusk flank under the northward IMF dominant condition. The dependence on IMF Bz is globally positive under the northward IMF dominant condition, whereas the dependence is negative in the near-Earth premidnight region under the southward IMF dominant condition. Both shortest and longest time lags increase from the mid-tail to the near-Earth premidnight region under the southward IMF dominant condition. On the other hand, the shortest (longest) time lag increases antisunward (sunward) along flanks under the northward IMF dominant condition. These features can be explained in terms of reconnection and Kelvin-Helmholtz diffusion mechanisms for entry of magnetosheath plasma into the plasma sheet and electric and magnetic drift transport in the plasma sheet.