Foreshock Ion Motion Across Discontinuities: Formation of Foreshock Transients
Foreshock Ion Motion Across Discontinuities: Formation of Foreshock Transients
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DOI：
10.1029/2022ja031161
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发表时间：
2023-04
期刊：
影响因子：
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通讯作者：
T. Liu;V. Angelopoulos;A. Vu;Hui Zhang
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文献类型：
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作者：
T. Liu;V. Angelopoulos;A. Vu;Hui Zhang
在离子前震中，热流异常(HFA)和前震气泡(FBS)是波动最强的两种前震瞬变现象，它们可以扰动磁层-电离层系统，提高激波加速效率。它们是由于前震离子和太阳风间断相互作用而形成的：前震离子驱动电流的方向以及它是减小还是增加了间断后面的磁场强度，决定了瞬变的形成是可以促进还是被抑制。因此，为了预报HFA和FB的形成及其对空间天气的影响，有必要预报前震离子驱动流的方向。在这项研究中，我们推导了不连续面内前震离子速度的解析方程来估计前震离子驱动的电流方向，这为HFA和FB的形成提供了一个定量的判据。为了验证这一判据，我们使用了月亮与太阳相互作用的加速重联湍流和电动力学来观测原始的太阳风不连续，并计算了不连续参数。我们用磁层多尺度观测了不连续面周围的前震离子运动，结果表明这些数据支持我们的模型。这项研究是建立HFA和FB形成预测模型的又一步，这样我们就可以利用月球轨道或L1上的太阳风观测来预测它们在地球上的空间天气影响。
In the ion foreshock, hot flow anomalies (HFAs) and foreshock bubbles (FBs) are two types of foreshock transients that have the strongest fluctuations, which can disturb the magnetosphere‐ionosphere system and increase shock acceleration efficiency. They form due to interaction between the foreshock ions and solar wind discontinuities: the direction of the foreshock ion‐driven current and whether it decreases or increases the magnetic field strength behind the discontinuity determine whether the transient's formation can be promoted or suppressed. Thus, to predict the HFA and FB formation and forecast their space weather effects, it is necessary to predict the foreshock ion‐driven current direction. In this study, we derive analytical equations of foreshock ion velocities within discontinuities to estimate foreshock ion‐driven current direction, which provides a quantitative criterion of HFA and FB formation. To validate the criterion, we use Acceleration Reconnection Turbulence & Electrodynamics of Moon's Interaction with the Sun to observe pristine solar wind discontinuities and calculate discontinuity parameters. We use Magnetospheric Multiscale to observe the foreshock ion motion around the discontinuities and show that the data support our model. This study is another step toward a predictive model of HFA and FB formation so that we can forecast their space weather effects at Earth using solar wind observations at lunar orbit or L1.