The storm-time ionospheric-thermospheric (IT) state is of great interest, since the IT dynamics change dramatically as energy is input and dissipated in the upper atmosphere. Lagrangian coherent structures (LCSs), which are objective ridges in time-evolving flows that describe the tendency of neighboring fluid elements to separate, provides a unique opportunity to infer the dynamics in the IT system. In this work, we model IT flows with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model and identify the LCSs. We compare the LCSs in the neutral winds and plasma drifts during quiet times versus during active times. We find that LCSs are largely aligned in the modeled IT flows, with a dawn-dusk asymmetry in their latitudinal position. During a geomagnetic storm, the thermospheric LCSs (T-LCSs) and ionospheric LCSs (I-LCSs) shift equatorward, align more closely with each other, and maintain a dawn-dusk asymmetry. The collocation of T-LCSs and I-LCSs and their analogous response to the geomagnetic storm provide evidence of energy input into the thermosphere and ionosphere simultaneously, and the ion drag is the dominant effect causing LCS alignment during a geomagnetic storm.

中文翻译：

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高纬度电离层和热层拉格朗日相干结构的排列

风暴时间电离层-热层 (IT) 状态非常有趣，因为随着能量在高层大气中输入和消散，IT 动态发生了巨大变化。拉格朗日相干结构 (LCS) 是随时间演化的流动中的客观脊，描述了相邻流体元素分离的趋势，为推断 IT 系统中的动力学提供了独特的机会。在这项工作中，我们使用热层-电离层-电动力学一般环流模型对 IT 流进行建模，并确定 LCS。我们比较了安静时期和活跃时期的中性风和等离子体漂移中的 LCS。我们发现 LCS 在建模的 IT 流程中基本上是一致的，在它们的纬度位置具有黎明-黄昏的不对称性。在地磁风暴期间，热层 LCS (T-LCS) 和电离层 LCS (I-LCS) 向赤道移动，彼此更紧密地对齐，并保持黎明-黄昏的不对称。T-LCSs 和 I-LCSs 的搭配及其对地磁暴的类似响应提供了能量同时输入热层和电离层的证据，离子阻力是导致地磁暴期间 LCS 对齐的主要影响。