Modeling the Expansion Speed of Foreshock Bubbles
Modeling the Expansion Speed of Foreshock Bubbles
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DOI：
10.1029/2022ja030814
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发表时间：
2023-01
期刊：
影响因子：
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通讯作者：
T. Liu;A. Vu;Hui Zhang;X. An;V. Angelopoulos
中科院分区：
文献类型：
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作者：
T. Liu;A. Vu;Hui Zhang;X. An;V. Angelopoulos
前震瞬变，包括热流异常（HFA）和前震泡（FB），经常观察到的离子前震。它们显著的动压扰动可以干扰弓形激波，导致磁层和电离层的扰动。它们也可以在其母弓形激波处对粒子加速作出贡献。然而，这些由前震瞬变引起的扰动和粒子加速还无法预测。在这项研究中，我们迈出了第一步，为FB（比HFA更简单）建立一阶预测扩张速度模型。从前震离子向太阳风离子的能量转换入手，导出了FB在形成初期和膨胀后期的膨胀速度随前震和太阳风参数的变化关系。我们使用具有不同参数的局部混合模拟来拟合和改进早期模型，并使用一维粒子模拟来测试后期模型。通过将模型结果与磁层多尺度（MMS）和亚暴期间事件和大尺度相互作用的时间历史（THEMIS）观测结果进行比较，我们调整了后期模型，并表明它可以预测FB扩张速度。我们的研究为前震瞬态形成和扩展的预测模型提供了基础，因此我们最终可以预测它们的空间天气效应和冲击时的粒子加速。
Foreshock transients, including hot flow anomalies (HFAs) and foreshock bubbles (FBs), are frequently observed in the ion foreshock. Their significant dynamic pressure perturbations can disturb the bow shock, resulting in disturbances in the magnetosphere and ionosphere. They can also contribute to particle acceleration at their parent bow shock. These disturbances and particle acceleration caused by the foreshock transients are not yet predictable, however. In this study, we take the first step in establishing a first‐order predictive expansion speed model for FBs (which are simpler than HFAs). Starting with energy conversion from foreshock ions to solar wind ions, we derive the FB expansion speed in the FB's early formation stage and late expansion stage as a function of foreshock and solar wind parameters. We use local hybrid simulations with varying parameters to fit and improve the early stage model and 1D particle‐in‐cell simulations to test the late‐stage model. By comparing model results with Magnetospheric Multiscale (MMS) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations, we adjust the late‐stage model and show that it can predict the FB expansion speed. Our study provides a foundation for predictive models of foreshock transient formation and expansion, so that we can eventually forecast their space weather effects and particle acceleration at shocks.