Interplanetary sources of magnetic storms: A statistical study
Interplanetary sources of magnetic storms: A statistical study
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DOI：
10.1029/2001ja000004
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发表时间：
2001-12
影响因子：
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通讯作者：
S. Vennerstroem
中科院分区：
文献类型：
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作者：
S. Vennerstroem
磁暴主要是由行星际介质中出现强烈的南向磁场引起的。这些磁场可以由太阳抛出的磁性结构直接形成，也可以由太阳风传播过程中的流相互作用过程直接形成。在这项研究中，我们检查了30年来对磁暴期间太阳风的卫星测量，目的是估计这两个过程的相对重要性。为了在统计上区分这两个过程，我们使用了太阳风质子温度相对于太阳风速Tp/Texp的经验关系式所期望的温度，以及速度梯度和黄道中的行星际磁场方位角。我们发现，流相互作用引起的压缩至少与强场抛射的直接效应一样重要，甚至可能更重要。只有大约20%-25%的大风暴小时和10%-15%的中风暴小时与满足Tp/Texp<；0.5标准的太阳风直接相关，这一标准以前被发现是喷发物质的良好指示器。超过50%的风暴小时是由太阳风引起的，相对于观测到的速度，太阳风具有更高的质子温度，并且在黄道面上具有明显的磁场花园方向的痕迹。
Magnetic storms are mainly caused by the occurrence of intense southward magnetic fields in the interplanetary medium. These fields can be formed directly either by ejection of magnetic structures from the Sun or by stream interaction processes during solar wind propagation. In the present study we examine 30 years of satellite measurement of the solar wind during magnetic storms, with the aim of estimating the relative importance of these two processes. We use the solar wind proton temperature relative to the temperature expected from the empirical relation to the solar wind speed Tp/Texp, together with the speed gradient, and the interplanetary magnetic field azimuth in the ecliptic, in order to distinguish between the two processes statistically. We find that compression due to stream interaction is at least as important as the direct effect of ejection of intense fields, and probably more so. Only around 20–25% of major and large storm hours and 10–15% of medium and small storm hours are directly associated with a solar wind meeting the criteria Tp/Texp < 0.5, a criteria which previously has been found to be a good indicator of ejected material. More than 50% of the storm hours are caused by a solar wind having an enhanced proton temperature relative to what is expected on the basis of the observed speed and having clear traces of gardenhose orientation of the magnetic field in the ecliptic plane.