高密度极尖区的形成原因

doi:10.6038/cjg2020N0424

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摘要极尖区是太阳风进入磁层的一个重要窗口，极尖区密度是反映这一物理过程的重要参量，通常情况下极尖区密度约为1~10 cm^-3，但有时卫星会观测到密度大于40 cm^-3的极尖区，本文称之为高密度极尖区.我们分析了Cluster卫星2001—2009年的观测数据，在470个极尖区穿越中找到28个高密度极尖区穿越事件并进行了统计研究，分析了高密度极尖区事件的形成原因，进而讨论了太阳风高效地进入极尖区的外部条件.结果表明：距正午的距离（｜MLT-12｜）较小，太阳风的密度高，低纬有磁层顶磁重联发生以及正偶极倾角都是观测到高密度极尖区事件的有利条件，并且当同时满足上述4个条件时，高密度极尖区事件发生率为100%；而低纬磁层顶磁重联以及大的正偶极倾角被认为是太阳风高效地进入极尖区的重要条件.这些研究结果有助于我们更进一步地理解太阳风进入极尖区的物理机制.

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	肖超
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关键词 ：极尖区, 高数密度, 偶极倾角, 太阳风

Abstract：The cusp region is an important window for solar wind particles entering the magnetosphere. Its density is a key parameter for understanding this physical process. Generally, the density of cusp region is about 1~10 cm^-3, but sometimes the satellites can observe cusp density greater than 40 cm^-3, which is called high-density cusp region in this paper. Based on the observations of Cluster satellite from 2001 to 2009, we find 28 high-density cusp crossing events in all the 470 cusp crossing events. We further discuss the favorable conditions of the formation of high-density cusp region, and the external conditions for solar wind efficiently entering cusp region. The results show that the smaller the ｜MLT-12｜, the higher the solar wind density, the existence of low latitude magnetopause reconnection and the positive dipole tilt are favorable conditions for the occurrence of high-density cusp events. When the above-mentioned four conditions are met at the same time, the occurrence rate of high-density cusp events is 100%. The low latitude magnetopause reconnection and large positive dipole tilt are considered as important conditions for the solar wind efficiently entering the cusp region. These results will help us to further understand the physical mechanism of the solar wind entering the cusp region.

Key words： Cusp High number density Dipole tilt Solar wind

收稿日期: 2020-01-02

PACS:	P353
	P354

基金资助:国家自然科学基金项目（41821003，41974194，41574154）资助.

通讯作者: 刘文龙,男,1980年生,博士,研究员,研究方向为空间物理.E-mail:liuwenlong@buaa.edu.cn E-mail: liuwenlong@buaa.edu.cn

作者简介: 肖超,男,1990年生,博士研究生,研究方向为空间物理.E-mail:chaoxiao@buaa.edu.cn

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http://www.geophy.cn//CN/10.6038/cjg2020N0424 或 http://www.geophy.cn//CN/Y2020/V63/I9/3231

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