A statistical study of the geoeffectiveness of magnetic clouds during high solar activity years
A statistical study of the geoeffectiveness of magnetic clouds during high solar activity years
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DOI：
10.1029/2004ja010410
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发表时间：
2003-12
影响因子：
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通讯作者：
Jichun Zhang;M. Liemohn;J. Kozyra;B. Lynch;T. Zurbuchen
中科院分区：
文献类型：
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作者：
Jichun Zhang;M. Liemohn;J. Kozyra;B. Lynch;T. Zurbuchen
[1]利用1998年1月1日至2002年4月30日期间太阳风磁场和等离子体资料，对磁层顶电流影响校正后的Dst值（Dst*）进行了统计分析，研究了271个磁暴（Dst* ≤-30 nT）与104个磁云的关系。研究发现，大部分磁云都是磁暴的起因，但只有30%的磁暴是由磁云引起的。风暴可以由云的各个区域或它们的组合以不同的发生百分比驱动。这些百分比也随着地磁活动水平的变化而变化。据发现，领先的领域是最geoeffective区域和鞘区是同样有效的，在太阳活动最大（42%）相比，太阳活动最小（43%）的磁暴的磁云引起的风暴的百分比。云引起的强风暴发生率为72%，远高于云引起的较小风暴发生率的20%。它还发现，“单极Bz”和“双极Bz”云有不同的地理有效性百分比，取决于Bz方向。这项研究的结果支持了长期以来人们所知的磁场活动主要受向南的Bz控制的观点。结果还表明，多步发展的风暴不仅可以由鞘场和云场的组合产生，也可以由云中不同的场产生。一个新的名称，准云，提出了那些云状的太阳风结构，显示出相对有组织的场旋转的证据。
[1] Using the Dst value corrected for the effects of magnetopause currents (Dst*) and solar wind magnetic field and plasma data from 1 January 1998 to 30 April 2002, during elevated solar conditions, we have statistically examined the relationship of 271 storms (Dst* ≤ −30 nT) to 104 magnetic clouds. It is found that most of the magnetic clouds result in geomagnetic storms, but only about 30% of storms are due to magnetic clouds. A storm can be driven by a cloud's various regions or their combinations with dissimilar occurrence percentages. These percentages change as a function of geomagnetic activity levels as well. It is found that the leading field is the most geoeffective region and the sheath region is equally effective at causing magnetic storms during solar maximum (42%) compared to solar minimum (43%) as a percentage of magnetic cloud-induced storms. The occurrence percentage of intense storms caused by clouds is 72%, which is much higher than the ∼20% occurrence percentage of smaller storms caused by clouds. It is also found that “unipolar Bz” and “bipolar Bz” clouds have different geoeffectiveness percentages, depending on the Bz orientation. The long-known control of magnetic activity mainly by southward Bz is supported by the results of this study. It is also shown that multistep development storms can result not only from both the combinations of sheath and cloud fields but also from different fields within a cloud. A new name, quasi-cloud, is proposed for those cloud-like solar wind structures which show evidence of relatively organized field rotations.