Auroral activity associated with unsteady magnetospheric erosion: Observations on December 18, 1990
Auroral activity associated with unsteady magnetospheric erosion: Observations on December 18, 1990
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与不稳定磁层侵蚀相关的极光活动：1990 年 12 月 18 日的观测
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发表时间：
1998
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影响因子：
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通讯作者：
W. Denig
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作者：
P. Sandholt;C. Farrugia;M. Øieroset;P. Stauning;W. Denig
我们报告极光观测1990年12月18日，当行星际条件应导致大规模侵蚀的昼侧磁层在亚暴增长阶段。行星际磁场（IMF）持续了很长一段时间的强指向北，之后又出现了几个小时的强指向南的IMF。指向南方的IMF的间隔被一些IMF方向的不连续性打断，在此期间，IMF南北分量Bz突然改变极性。在新奥勒松（磁纬75 °）由子午线扫描光度计和全天空照相机监测的极光响应如下：负IMF Bz的间隔的特征是日侧尖点/裂缝极光的赤道边界向赤道方向的净迁移，正如以前的研究所预期的那样。然而，在这种情况下，我们发现纬向移动是逐步发生的，包括最初在MLAT 0.5 °赤道方向上的单个极光事件的增亮，随后是通常持续4 - 5分钟的稳定的向极后退。IMF Bz <0条件的第一个小时的净效应是将赤道边界向地磁赤道移动了MLAT 0.27 °。极光数据表明，在这种情况下，昼侧磁层侵蚀间歇性地发生：重联的爆发（最初的增亮）之后是重联电场的关闭（随后的向极撤退）。重联的爆发可以用通量转移事件或等效的通量侵蚀事件来识别。
We report auroral observations made on December 18, 1990, when interplanetary conditions should lead to large-scale erosion of the dayside magnetosphere during a substorm growth phase. A long interval of strongly northward pointing interplanetary magnetic field (IMF) was succeeded by several hours of strongly southward pointing IMF. The interval of southward pointing IMF was punctuated by a number of IMF directional discontinuities during which the IMF north-south component, Bz changed polarity abruptly. The auroral responses, monitored at Ny Alesund (75° magnetic latitude) by meridian scanning photometers and all-sky cameras, were as follows: The interval of negative IMF Bz was characterized by a net equatorward migration of the equatorward boundary of the dayside cusp/cleft aurora, as expected from previous studies. On this occasion, however, we find that the latitudinal shift occurred in steps which consisted of an initial brightening of individual auroral events at ∼0.5° MLAT equatorward of the preexisting luminosity, followed by a steady poleward retreat lasting typically 4–5 min. The net effect over the first hour of IMF Bz < 0 conditions was to move the equatorward boundary toward the geomagnetic equator by ∼2.7° MLAT. The auroral data suggest that in this instance dayside magnetosphere erosion took place intermittently: bursts of reconnection (initial brightenings) are followed by a switch-off of the reconnection electric field (subsequent poleward retreat). The bursts of reconnection may be identified with flux transfer events or, equivalently, flux erosion events.