Statistical Study of Magnetosheath Jet‐Driven Bow Waves
Statistical Study of Magnetosheath Jet‐Driven Bow Waves
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DOI：
10.1029/2019ja027710
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发表时间：
2020-02
期刊：
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通讯作者：
T. Liu;H. Hietala;V. Angelopoulos;Y. Omelchenko;R. Vainio;F. Plaschke
中科院分区：
文献类型：
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作者：
T. Liu;H. Hietala;V. Angelopoulos;Y. Omelchenko;R. Vainio;F. Plaschke
当磁鞘喷流（局部动态压力增强）以比局部磁音速更快的（相对）速度压缩周围磁鞘时，可以在喷流前方形成弓形波或激波。最近观察到这种弓形波或激波可以加速粒子，从而有助于地球弓形激波扩展环境中的磁鞘加热和粒子加速。为了进一步了解射流驱动的弓形波的特征，我们进行了一项统计研究，以检查哪些太阳风条件有利于它们的形成，以及它们是否经常加速粒子。我们确定了2,859个磁鞘喷流中的364个（约13%）在它们前面有一个弓形波或激波，马赫数通常大于1.1。我们发现，大的太阳风等离子体β，弱的行星际磁场（IMF）强度，大的太阳风阿尔文马赫数，和强大的太阳风动压，它们的形成提供了有利的条件。我们还表明，磁鞘射流与弓波或冲击更频繁地与更高的最大离子和电子能量比那些没有他们，确认这是常见的这些结构，以加速粒子。特别是，磁鞘射流与弓波的电子能量通量平均增强的2倍相比，那些没有弓波和周围的磁鞘。我们的研究表明，磁鞘喷流可以促进粒子的激波加速，特别是对于高马赫数激波。因此，激波模型应该推广到包括磁鞘喷流和伴随的粒子加速。
When a magnetosheath jet (localized dynamic pressure enhancements) compresses ambient magnetosheath at a (relative) speed faster than the local magnetosonic speed, a bow wave or shock can form ahead of the jet. Such bow waves or shocks were recently observed to accelerate particles, thus contributing to magnetosheath heating and particle acceleration in the extended environment of Earth's bow shock. To further understand the characteristics of jet‐driven bow waves, we perform a statistical study to examine which solar wind conditions favor their formation and whether it is common for them to accelerate particles. We identified 364 out of 2,859 (~13%) magnetosheath jets to have a bow wave or shock ahead of them with Mach number typically larger than 1.1. We show that large solar wind plasma beta, weak interplanetary magnetic field (IMF) strength, large solar wind Alfvén Mach number, and strong solar wind dynamic pressure present favorable conditions for their formation. We also show that magnetosheath jets with bow waves or shocks are more frequently associated with higher maximum ion and electron energies than those without them, confirming that it is common for these structures to accelerate particles. In particular, magnetosheath jets with bow waves have electron energy flux enhanced on average by a factor of 2 compared to both those without bow waves and the ambient magnetosheath. Our study implies that magnetosheath jets can contribute to shock acceleration of particles especially for high Mach number shocks. Therefore, shock models should be generalized to include magnetosheath jets and concomitant particle acceleration.