Interplanetary circumstances of quasi-perpendicular interplanetary shocks in 1996-2005
Interplanetary circumstances of quasi-perpendicular interplanetary shocks in 1996-2005
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DOI：
10.1029/2009ja015039
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发表时间：
2010-07
影响因子：
--
通讯作者：
I. Richardson;H. Cane
中科院分区：
文献类型：
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作者：
I. Richardson;H. Cane
[1]行星际激波阵面的法线与上游磁场方向之间的夹角（θBn），虽然通常被认为是“激波”的一个属性，但也由激波上游磁场的结构决定。我们研究了1996-2005年期间105个近地准垂直激波的行星际环境，这些激波由θBn ≥ 80°和/或激波漂移粒子加速的证据确定。这些激波中约有87%是由行星际日冕物质抛射（ICME）驱动的;其余的可能是共转相互作用区域的前向激波。对于大约一半的冲击，上游场近似垂直于径向，或者是东西向，或者是东西向，或者是高度倾斜于黄道。这样的场方向将给出径向传播激波的准垂直构形。在观测时，大约30%的冲击是通过ICME传播的，或者紧随其后。另外四分之一是通过日光层等离子体片（HPS）传播的，还有四分之一发生在没有HPS特征的缓慢太阳风中。在高速气流中观察到大约11%，在其他冲击后的鞘中观察到7%。在高速流中发现的冲击的比例大约是基于在地球上观察到这种流的时间比例而预期的三分之一。准垂直激波通过ICME的频率比预期的高出2-3倍。此外，通过ICME传播的激波比ICME外的激波更可能具有更大的θBn值。
[1] The angle (θBn) between the normal to an interplanetary shock front and the upstream magnetic field direction, though often thought of as a property “of the shock,” is also determined by the configuration of the magnetic field immediately upstream of the shock. We investigate the interplanetary circumstances of 105 near-Earth quasi-perpendicular shocks during 1996–2005 identified by θBn ≥ 80° and/or by evidence of shock drift particle acceleration. Around 87% of these shocks were driven by interplanetary coronal mass ejections (ICMEs); the remainder were probably the forward shocks of corotating interaction regions. For around half of the shocks, the upstream field was approximately perpendicular to the radial direction, either east-west or west-east or highly inclined to the ecliptic. Such field directions will give quasi-perpendicular configurations for radially propagating shocks. Around 30% of the shocks were propagating through, or closely followed, ICMEs at the time of observation. Another quarter were propagating through the heliospheric plasma sheet (HPS), and a further quarter occurred in slow solar wind that did not have characteristics of the HPS. Around 11% were observed in high-speed streams, and 7% in the sheaths following other shocks. The fraction of shocks found in high-speed streams is around a third of that expected based on the fraction of the time when such streams were observed at Earth. Quasi-perpendicular shocks are found traveling through ICMEs around 2–3 times more frequently than expected. In addition, shocks propagating through ICMEs are more likely to have larger values of θBn than shocks outside ICMEs.