Observations of plasma sheet dynamics earthward of the onset region with the Geotail spacecraft
Observations of plasma sheet dynamics earthward of the onset region with the Geotail spacecraft
复制标题
使用 Geotail 航天器观测起始区域的地球等离子体片动力学
DOI：
10.1029/2000ja000419
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发表时间：
2001
影响因子：
--
通讯作者：
T. Mukai
中科院分区：
文献类型：
--
作者：
L. Frank;W. Paterson;J. Sigwarth;T. Mukai
在1996年8月14日约0406UT的极光亚暴爆发期间，GeoTail航天器的位置非常接近赤道平面上相应的不稳定区域，这是由提供极光电离层测绘的全球地磁场模型确定的。极地号航天器上的地球相机被用来获取全球极光图像。环电流中的磁场被赤道电流片充分拉伸，使得GeoTail航天器在10.2RE处的径向位置是起始区的地球。在几分钟内以200公里/S的速度向地球流动，与先前存在的极光椭圆形局部区域的初始亮度一致。这种极光光度随后在几分钟内下降，没有一个很好的膨胀阶段；也就是说，发生了“假爆发”。随着这一开始，磁场发生了部分双极化，以及大规模的磁波动，这种波动一直持续到0413UT时极光椭圆形上的另一个黑点变亮。当极光光度在0424UT左右进入恢复阶段时，随着一个发育良好的膨胀阶段的结束，这些波动停止了。在0420UT的短膨胀阶段开始时，On磁力仪在径向距离为6.6RE的情况下记录到了一个主要的磁场偶极，因为热等离子体向地球移动的注入锋穿过了地尾位置。目前对不稳定区地面起始区现象的观测与以前报道的环电流不稳定性尾部等离子体和磁场的测量相结合，以便开始勾画起始区几个动力学特征之间的关系。
During the onset of an auroral substorm at about 0406 UT on August 14, 1996, the position of the Geotail spacecraft was located very near the corresponding region of instability in the equatorial plane as determined with a global model of the geomagnetic fields which provided the mapping from the auroral ionosphere. The Earth Camera on board the Polar spacecraft was used to acquire the global auroral images. The magnetic fields in the ring current were sufficiently stretched by the equatorial current sheet such that the radial position of the Geotail spacecraft at 10.2 RE was earthward of the onset region. Earthward flows at speeds in the range of 200 km/s for a period of several minutes were coincident with the initial brightening of a localized region of the previously existing auroral oval. This auroral luminosity subsequently declined within several minutes without a well-developed expansive phase; that is, a “pseudo-onset” occurred. Partial dipolarization of the magnetic fields occurred with this onset as well as large-scale magnetic fluctuations which continued through the brightening of another spot on the auroral oval at 0413 UT. These fluctuations ceased with the end of a well-developed expansive phase at about 0424 UT, when the auroral luminosities entered their recovery phase. At the beginning of the short expansive phase at 0420 UT the magnetometer on GOES 8 at a radial distance of 6.6 RE recorded a major dipolarization of the magnetic fields as an earthward moving injection front of hot plasma passed across the Geotail position. The present observations of the onset phenomena earthward of the instability region are combined with previously reported measurements of plasmas and magnetic fields at distances tailward of the instability in the ring current in order to begin sketches of the relationship among several dynamical features of the onset region.