压力梯度在驱动向阳磁鞘流和磁层顶运动中的作用
The role of pressure gradients in driving sunward magnetosheath flows and magnetopause motion
摘要：
虽然压力平衡可以预测磁层顶对上游压力变化的响应将移动多远，但它不能确定瞬态响应的速度。使用亚暴（THEMIS）过程中的事件和大尺度相互作用的时间历史，我们提出了多点观测揭示，第一次，强（热+磁）压力梯度的磁鞘由于前震瞬态，最有可能的热流异常（HFA），这降低了总压力上游的弓激波。通过将航天器的时间序列转换成空间图像，我们定量地表明，这些压力梯度引起所观察到的加速等离子体，导致快速向阳磁鞘流的磁层顶的局部向外扭曲之前。磁鞘等离子体的加速足够快，使磁层顶隆起的峰值保持在接近平衡的位置，即压力平衡。因此，我们表明，在磁鞘中的压力梯度，由于总压力的瞬态变化，上游可以直接驱动异常流，反过来是重要的信息传输从弓形激波的磁层顶。
英文摘要：
While pressure balance can predict how far the magnetopause will move in response to an upstream pressure change, it cannot determine how fast the transient reponse will be. Using Time History of Events and Macroscale Interactions during Substorms (THEMIS), we present multipoint observations revealing, for the first time, strong (thermal + magnetic) pressure gradients in the magnetosheath due to a foreshock transient, most likely a Hot Flow Anomaly (HFA), which decreased the total pressure upstream of the bow shock. By converting the spacecraft time series into a spatial picture, we quantitatively show that these pressure gradients caused the observed acceleration of the plasma, resulting in fast sunward magnetosheath flows ahead of a localised outward distortion of the magnetopause. The acceleratation of the magnetosheath plasma was fast enough to keep the peak of the magnetopause bulge at approximately the equilibrium position i.e. in pressure balance. Therefore, we show that pressure gradients in the magnetosheath due to transient changes in the total pressure upstream can directly drive anomalous flows and in turn are important in transmitting information from the bow shock to the magnetopause.
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