Interplanetary origin of multiple‐dip geomagnetic storms
Interplanetary origin of multiple‐dip geomagnetic storms
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DOI：
10.1029/2008ja013228
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发表时间：
2008-03
影响因子：
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通讯作者：
Jie Zhang;I. Richardson;D. Webb
中科院分区：
文献类型：
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作者：
Jie Zhang;I. Richardson;D. Webb
[1]本文系统地研究了1996-2006年强磁暴（Dst ≤-100 nT）期间大磁倾角的行星际驱动因素。大倾角被定义为Dst指数暂时下降，幅度大于14.5 nT。如果地球有效太阳风的区域具有强大的南向磁场，被地球有效太阳风较少的太阳风分隔开，则多次下降会导致风暴。在这90个强风暴中，我们发现只有34%（31个事件）显示出经典的“一个倾角”的轮廓，而49%（44个事件）有两个倾角。另外17%（15起事件）有三次或三次以上的下降。我们发现，在与90个风暴相关的总共165个主要倾角中，约45%（74个倾角）是由行星际日冕物质抛射（ICME）或抛射物引起的，30%（49个倾角）是由位于ICME驱动的冲击和ICME前缘之间的鞘（SH）引起的。约7%（11次下降）是由ICME进入前一ICME并增强其磁场（PICME-SH）驱动的冲击引起的。大约11%（18个下降）是由于来自冕洞的高速太阳风与先前较慢的太阳风相互作用而形成的共转相互作用区（CIR）。另有7%（12次下降）是由风暴爆发前的各种太阳风结构造成的。在这些不同类型的驱动因素中，平均而言，最大的风暴倾角是由通过先前ICME（PICME-SH）传播的冲击产生的。两次下沉风暴的一个常见原因是第一次下沉由上游鞘层产生，第二次下沉由驱动ICME产生。二次磁暴或多次磁暴的另一个常见原因是在复杂的太阳风流动中存在多个向南磁场分区，这是由两个连续的、间隔很近的ICME造成的。
[1] In this paper, we have systematically investigated the interplanetary drivers of major dips during intense (Dst ≤ −100 nT) geomagnetic storms in 1996–2006. A major dip is defined as a temporary decrease in Dst index with amplitude larger than 14.5 nT. Multiple dips result in a storm if regions of geoeffective solar wind with strong southward magnetic fields are separated by less geoeffective solar wind. Among these 90 intense storms, we found that only 34% (31 events) showed a classical “one-dip” profile, while 49% (44 events) had two dips. Another 17% (15 events) had triple or more dips. We found that of a total of 165 major dips associated with the 90 storms, about 45% (74 dips) were caused by interplanetary coronal mass ejections (ICMEs), or ejecta, and 30% (49 dips) were caused by sheaths (SHs) that lie between shocks driven by ICMEs and leading edges of the ICMEs. About 7% (11 dips) were caused by a shock driven by an ICME running into a preceding ICME and intensifying its magnetic field (PICME-SH). About 11% (18 dips) were due to corotating interaction regions (CIRs) formed by the interaction of high-speed solar wind from coronal holes with the preceding slower solar wind. Another 7% (12 dips) were caused by various solar wind structures prior the onset of the storm. Among these different types of drivers, the largest storms dips on average were produced by shocks propagating through preceding ICMEs (PICME-SH). One frequent cause of a two-dip storm is that the first dip is produced by the upstream sheath and the second dip is produced by the driving ICME. Another common cause of a two-dip or multiple-dip storm is the presence of multiple subregions of southward magnetic field within a complex solar wind flow, resulting from two successive, closely spaced ICMEs.