Two‐dimensional observations of overshielding during a magnetic storm by the Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar
Two‐dimensional observations of overshielding during a magnetic storm by the Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar
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DOI：
10.1029/2007ja012641
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发表时间：
2008
影响因子：
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通讯作者：
Y. Ebihara;N. Nishitani;T. Kikuchi;T. Ogawa;K. Hosokawa;M. Fok
中科院分区：
文献类型：
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作者：
Y. Ebihara;N. Nishitani;T. Kikuchi;T. Ogawa;K. Hosokawa;M. Fok
首次报道了可能由过屏蔽引起的电离层等离子体流动的二维观测结果。在2006年12月15日的强磁暴期间，中纬度超级双极光雷达网在日本北海道雷达进行了观测。在风暴的主要阶段，磁层连续暴露在向南的行星际磁场（IMF）下数小时。紧接着国际货币基金组织向北转向，在磁极纬度50°-60°的黄昏前区域观测到反太阳等离子体流，持续约14分钟，最大视距速度达到70-80米/秒。这些特征与环电流和电离层之间的耦合与过屏蔽条件的模拟是一致的。在第一次观测的1小时内，在向南的IMF期间观察到类似的反向阳流。然而，在这种情况下，模拟不能解释反向太阳的流动。认为屏蔽/过屏蔽状况并非单纯由IMF北转所致。第二种类似过屏蔽的情况可归因于与亚暴有关的极帽的突然收缩，或由于磁层离子的突然注入而转换的惯性电流的突然加强。然而，两者都不能完全解释观察结果。
[1] Two-dimensional observations of ionospheric plasma flows possibly caused by overshielding are reported for the first time. The observations were made by the midlatitude Super Dual Auroral Radar Network Hokkaido radar in Japan during a major magnetic storm on 15 December 2006. The magnetosphere was exposed continuously to a southward interplanetary magnetic field (IMF) for several hours during the main phase of the storm. Immediately following the subsequent northward turning of the IMF, an antisunward plasma flow was observed for about 14 min in the predusk sector at magnetic latitudes of 50°–60°, reaching a maximum line-of-sight speed of 70–80 m/s. These features are consistent with a simulation of coupling between the ring current and the ionosphere associated with an overshielding condition. Within 1 h of the first observation, a similar antisunward flow was observed during a period of southward oriented IMF. However, the simulation cannot account for the antisunward flow in this case. It is suggested that the shielding/overshielding condition is not simply caused by the northward turning of IMF. This second overshielding-like condition is attributable to a sudden contraction of the polar cap associated with the substorm or to a sudden strengthening of the inertial current converted from the abrupt injection of magnetospheric ions. However, neither fully accounts for the observations.