Polar cap area and boundary motion during substorms
Polar cap area and boundary motion during substorms
复制标题
DOI：
10.1029/1998ja900097
复制
发表时间：
1999-06
影响因子：
--
通讯作者：
M. Brittnacher;M. Fillingim;G. Parks;J. Spann
中科院分区：
文献类型：
--
作者：
M. Brittnacher;M. Fillingim;G. Parks;J. Spann
利用极地紫外线成像仪(UVI)在1997年1月三个亚暴期间不同星际磁场方向的图像测量了极冠面积随当地时间和亚暴阶段的变化。我们测量了极光椭圆形极冠面积的变化以及极光向极光和赤道方向边界的运动。结果表明，极冠边界受椭圆变薄、极冠结构减少、午夜亚暴向极地扩展以及仪器灵敏度阈值以下光度衰减的强烈影响。一般来说，这些影响主导着极光椭圆形在其赤道边缘的纬向运动。一个新的特征是，在亚暴增长阶段，极冠区清除了降水，这扩大了极冠区的大小，但不一定与开放通量区的扩大有关。另一个发现是，发生前极冠面积的增加可能与向南移动的国际货币基金组织部分的强度无关。1例极帽面积增大，而IMF向南分量为0±0.5nT。这些观测结果对使用极冠面积来估计波瓣磁场中的能量存储和亚暴期间损失的大小的模型有很大的影响。
The area of the polar cap as a function of local time and substorm phase was measured using images from the Polar Ultraviolet Imager (UVI) for different interplanetary magnetic field (IMF) orientations during three substorms in January 1997. We measured changes in the polar cap area and motion of the poleward and equatorward boundary of the auroral oval. It was found that the polar cap boundary is strongly influenced by thinning of the oval, decrease in polar cap structures, the poleward expansion of the substorm at midnight, and the fading of luminosity below the instrument sensitivity threshold. Generally, these effects dominate over the latitudinal motion of the auroral oval at its equatorward edge. A new feature is that the polar cap region clears of precipitation during the substorm growth phase, which expands the size of the polar cap but is not necessarily related to an expansion of the open flux region. Another finding is that the increase in polar cap area prior to onset can be independent of the strength of the southward IMF component. For one case the polar cap area increased while the southward component of the IMF was 0 ± 0.5 nT. These observations have strong implications for models that use the polar cap area to estimate the magnitude of energy storage in the lobe magnetic field and loss during substorms.