Auroral substorm timescales: IMF and seasonal variations
Auroral substorm timescales: IMF and seasonal variations
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极光亚暴时间尺度：IMF 和季节变化
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发表时间：
2004
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通讯作者：
J. Spann
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文献类型：
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作者：
D. Chua;G. Parks;M. Brittnacher;J. Spann
[1]极光亚暴活动的时间尺度和阶段的量化在这项研究中使用的半球功率计算极地紫外成像仪（UVI）的观测。用这种方法，我们能够确定亚暴阶段自我一致的UVI光学测量，而不需要任何辅助指标的极光活动。这种技术也使我们能够结合联合收割机的亚暴时间尺度的定量测量与定性描述极光形态在每个事件。我们展示了数百次亚暴事件的亚暴特征如何随IMF BZ方向和季节而变化。亚暴强度，作为测量的电子沉淀的能量沉积率，表现出更大的变化与IMF BZ方向比与季节。亚暴扩展的时间尺度与IMF BZ方向和季节的变化相当。另一方面，亚暴恢复时间随季节的变化比随IMF BZ方向的变化更大。亚暴活动的恢复时间是有序的，无论是夜侧极光区是阳光照射：亚暴发生在冬季和春分期间有类似的恢复时间尺度，这两个都大致是一个因素的两倍，比夏季时，极光椭圆是阳光照射。然而，国际货币基金组织的BZ方向有很强的调节作用，在夏季的亚暴扩展和恢复的时间尺度。冬夏不对称的极光以前的研究所描述的亚暴恢复时间尺度的季节性变化，在这项工作中的特点更完全地解释。我们的研究结果支持的假设，电离层起着积极的作用，在管理极光的动态。
[1] The timescales and phases of auroral substorm activity are quantified in this study using the hemispheric power computed from Polar Ultraviolet Imager (UVI) observations. With this approach we are able to determine substorm phase self consistently from the UVI optical measurements without needing any ancillary metrics for auroral activity. This technique also allows us to combine a quantitative measurement of substorm timescales with the qualitative description of auroral morphology during each event. We show how the characteristics of substorms vary with IMF BZ orientation and season for several hundred substorm events. Substorm intensity, as measured by the rate of energy deposition by electron precipitation, exhibits greater variation with IMF BZ orientation than with season. The timescale of substorm expansion shows comparable variation with both IMF BZ orientation and season. On the other hand, substorm recovery times vary more strongly with season than with IMF BZ direction. The recovery time for substorm activity is well ordered by whether or not the nightside auroral region is sunlit: substorms occurring in the winter and equinox periods have similar recovery timescales which are both roughly a factor of two longer than that for summer when the auroral oval is sunlit. However, IMF BZ orientation is shown to have a strong modulating effect on both substorm expansion and recovery timescales during the summer. The winter-summer asymmetries in the aurora described by previous studies are more completely explained by the seasonal variations of substorm recovery timescales characterized in this work. Our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora.