Cusp observations during a sequence of fast IMF BZ reversals
Cusp observations during a sequence of fast IMF BZ reversals
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DOI：
10.5194/angeo-27-2721-2009
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发表时间：
2009-07
影响因子：
1.9
通讯作者：
H. Cai;I. McCrea;M. Dunlop;J. Davies;Y. Bogdanova;F. Pitout;S. Milan;M. Lockwood;Shuying Ma
中科院分区：
文献类型：
--
作者：
H. Cai;I. McCrea;M. Dunlop;J. Davies;Y. Bogdanova;F. Pitout;S. Milan;M. Lockwood;Shuying Ma
抽象的。近年来，大量文献报道了行星际磁场Z分量（BZ）向北或向南条件下尖点对太阳风变化的响应。这些研究表明，时间和空间因素的重要性，在确定的范围和形态的尖点及其位置的变化，连接到重联几何形状的变化。在这里，我们提出了一个比较研究的尖点，集中在一个间隔的特点是一系列的快速逆转，在BZ主导的国际货币基金组织，从空间和地面仪器的观测为基础。在此期间，从2003年2月12日世界时08：00到12：00，IMF BZ分量经历了四次反转，每个方向保持约30分钟。当时，该集群航天器正处于穿过北方半球磁层的出轨轨道上，而EISCAT设施的大陆甚高频和斯瓦尔巴德（ESR）雷达正在运行，以支持该集群的使命。在间隔期间，Cluster和EISCAT有时都观察了尖点区域。一系列的国际货币基金组织的逆转导致了一系列的极向和赤道运动的尖点，因此集群越过高海拔尖点两次，最后退出向阳面磁层顶，两次条件下向北的国际货币基金组织BZ。所有四个星团航天器的第一次磁层尖点相遇，显示出典型的波瓣重连的反向离子弥散;随后，星团航天器1号和3号（仅）第二次穿过尖点。我们认为，在这第二个尖点交叉，这两个航天器很可能已经在新关闭的磁力线，这是第一次重新连接（打开）在低纬度，后来重新连接（重新关闭）极向北方尖点。在电离层高度，SuperDARN高频网络的ESR和Pykkvibaer雷达都清楚地捕捉到了尖点/裂缝区域响应一系列IMF极性变化的纬度偏移。根据高频雷达观测结果推断的开闭场线边界（OCB）随IMF极性的变化而发生纬向变化，这与纽韦尔等人（1989）的预测是一致的。此外，EISCAT甚高频和ESR雷达产生的电离层参数的变化与高频雷达观测得出的推论基本一致。我们的结论是，集群航天器1号和3号第二次越过尖点，作为响应IMF极性反转的尖点的纬向迁移的结果;然而，在那个时候，尖点位于航天器4的极向。来自DMSP两个卫星通道的尖点快照为这种解释提供了进一步的支持。
Abstract. In recent years, a large number of papers have reported the response of the cusp to solar wind variations under conditions of northward or southward Interplanetary Magnetic Field (IMF) Z-component (BZ). These studies have shown the importance of both temporal and spatial factors in determining the extent and morphology of the cusp and the changes in its location, connected to variations in the reconnection geometry. Here we present a comparative study of the cusp, focusing on an interval characterised by a series of rapid reversals in the BZ-dominated IMF, based on observations from space-borne and ground-based instrumentation. During this interval, from 08:00 to 12:00 UT on 12 February 2003, the IMF BZ component underwent four reversals, remaining for around 30 min in each orientation. The Cluster spacecraft were, at the time, on an outbound trajectory through the Northern Hemisphere magnetosphere, whilst the mainland VHF and Svalbard (ESR) radars of the EISCAT facility were operating in support of the Cluster mission. Both Cluster and the EISCAT were, on occasion during the interval, observing the cusp region. The series of IMF reversals resulted in a sequence of poleward and equatorward motions of the cusp; consequently Cluster crossed the high-altitude cusp twice before finally exiting the dayside magnetopause, both times under conditions of northward IMF BZ. The first magnetospheric cusp encounter, by all four Cluster spacecraft, showed reverse ion dispersion typical of lobe reconnection; subsequently, Cluster spacecraft 1 and 3 (only) crossed the cusp for a second time. We suggest that, during this second cusp crossing, these two spacecraft were likely to have been on newly closed field lines, which were first reconnected (opened) at low latitudes and later reconnected again (re-closed) poleward of the northern cusp. At ionospheric altitudes, the latitudinal excursions of the cusp/cleft region in response to the series of the IMF polarity changes were clearly captured by both the ESR and the Pykkvibaer radar of the SuperDARN HF network. The Open-Closed field-line Boundary (OCB) inferred from the HF radar observations underwent latitudinal variations in response to the IMF polarity changes that are in accordance with those predicted by Newell et al. (1989). Furthermore, variations in the ionospheric parameters yielded by the EISCAT VHF and ESR radars are basically consistent with inferences drawn from the HF radar observations. We conclude that Cluster spacecraft 1 and 3 crossed the cusp for a second time as a result of the latitudinal migration of the cusp in response to the IMF polarity reversals; at that time, however, the cusp lay poleward of spacecraft 4. Snapshots of the cusp from two DMSP satellite passes provide further support for this interpretation.