Timing and location of substorm onsets from THEMIS satellite and ground based observations
Timing and location of substorm onsets from THEMIS satellite and ground based observations
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DOI：
10.5194/angeo-27-2813-2009
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发表时间：
2009-07
影响因子：
1.9
通讯作者：
S. Mende;V. Angelopoulos;H. Frey;E. Donovan;B. Jackel;K. Glassmeier;J. Mcfadden;D. Larson;C. Carlson
中科院分区：
文献类型：
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作者：
S. Mende;V. Angelopoulos;H. Frey;E. Donovan;B. Jackel;K. Glassmeier;J. Mcfadden;D. Larson;C. Carlson
抽象的。THEMIS GBO站网络的前所未有的覆盖范围加上高的时间和空间分辨率，使我们能够确定亚暴爆发时光学极光全球规模发展的各个阶段。我们确定了亚暴开始极光现象的几个步骤，我们认为，最迅速的发展是亚暴极向扩展（SPE）的开始，它是最有用的亚暴开始的准确时间。这一步的物理意义是大气中大尺度亚暴能量耗散的开始，这是由于粒子降水和极光电喷流。我们还发现了几个前光标特征。我们还测量了与THEMIS卫星上相同亚暴相关的磁脉冲的到达时间。我们使用这些时间和一个简单的模型与假设的电离声速在300-800公里/秒的范围内计算的位置和时间的起源的磁脉冲传播从亚暴发病。假设亚暴发生在两颗THEMIS卫星之间，脉冲从一个奇异的起始点沿磁尾GSM-x轴沿着传播。这种技术仅在亚暴的地面特征在当地时间（或经度）非常接近THEMIS卫星场线底部的情况下才有用。计算出的原点的x距离自然高度依赖于假设的传播速度模型和相关的磁声速。三个事件的起始点的所得x距离范围在11和17.6 RE之间。表示需要高度拉伸的场线以映射到极光起始纬度的起始区域，但通常认为其对于中性线形成来说太近。相应的开始时间是在0至170秒的范围内，前SPE强烈依赖于假定的传播速度。
Abstract. The unprecedented coverage of the THEMIS GBO station network coupled with high temporal and spatial resolution allowed us to determine the various stages of the global scale developments of the optical aurora at substorm onsets. We identified several steps of the substorm onset auroral phenomena and we suggest that the most rapid development is the starting of the Substorm Poleward Expansion (SPE) and it is most useful for accurate timing of the substorm onset. The physical significance of this step is the start of the large scale substorm energy dissipation in the atmosphere due to particle precipitation and auroral electrojet currents. We also recognized several pre-cursor features. We also measured the time of arrival of magnetic impulses associated with the same substorms at the THEMIS satellites. We used these times and a simple model with assumed iono-acoustic speeds in the range of 300–800 km/s to calculate the location and time of the origin of the magnetic impulses propagating from substorm onset. The assumption was made that the substorm occurred between two THEMIS satellites and the impulses propagated away from a singular starting point in and out along the magneto tail GSM-x axis. This technique is only useful in cases where the ground based signature of the substorm is very close in local time (or longitude) to the foot of the field lines of the THEMIS satellites. The x distance of the calculated origins were naturally highly dependent on the assumed propagation velocity model and the associated magneto-sonic speed. The resulting x distances of the starting point for the three events ranged between 11 and 17.6 RE. denoting a starting region that requires highly stretched field lines to map to the auroral onset latitude but which is generally considered to be too close for neutral line formation. The corresponding start times were in the range of 0 to 170 s prior SPE depending strongly on the assumed propagation speed.