Ion-Scale Flux Rope Observed inside a Hot Flow Anomaly
Ion-Scale Flux Rope Observed inside a Hot Flow Anomaly
复制标题
在热流异常内部观察到的离子尺度通量绳
DOI：
10.1029/2019gl085933
复制
发表时间：
2020-03-16
影响因子：
5.2
通讯作者：
Wang, Mengmeng
中科院分区：
文献类型：
--
作者：
Bai, Shi-Chen;Shi, Quanqi;Wang, Mengmeng
我们报告了2016年12月17日磁层多尺度卫星星座在地球准平行弓形激波上游观测到的热流异常（HFA）后缘内嵌入的向地移动离子尺度通量绳。HFA的驱动器是一个切向不连续性，由Wind航天器在太阳风中观察到，周围没有通量绳特征。这表明向地运动的磁绳是在HFA内部产生的。这种离子尺度的磁绳不是一种无力结构，并且由于强磁压梯度力而膨胀。太阳风离子在磁绳内被静电场减速，静电场可能是由太阳风粒子的电荷分离引起的。我们的观测结果表明，磁场重联可能发生在HFA内部。重联和通量绳可能在前震瞬变中的粒子加速/加热中起作用。简明语言概要高能粒子经常在前震瞬变或前震区域内观察到。这些高能粒子的加速机制仍然是一个悬而未决的问题。目前已经提出了一些可能的加速机制，如费米加速、电子喷射、低杂波漂移不稳定性和磁重联等。然而，迄今为止，磁重联只发现在混合模拟的前震瞬变的产生，但从来没有在现场观测报告。在本文中，我们报告了一个离子尺度的磁通绳观测在后缘的热流异常，这可能会产生在磁场重联。我们的观测结果表明，重联可能发生在前震瞬变局部，并有助于他们的粒子加速。
We report an earthward moving ion-scale flux rope embedded within the trailing edge of a hot flow anomaly (HFA) observed by the Magnetospheric Multiscale satellite constellation on 17 December 2016 upstream of Earth's quasi-parallel bow shock. The driver of the HFA, a tangential discontinuity, was observed by the Wind spacecraft without flux rope signatures around it in the solar wind. This suggests that the earthward moving flux rope was generated inside the HFA. This ion-scale flux rope is not a force free structure and expands due to a strong magnetic pressure gradient force. Solar wind ions are decelerated inside the flux rope by the static electric field likely caused by the charge separation of solar wind particles. Our observations imply that magnetic reconnection may have occurred inside the HFA. Reconnection and flux ropes may play a role in particle acceleration/heating inside foreshock transients.Plain Language Summary Energetic particles are often observed inside the foreshock transients or in the foreshock region. The acceleration mechanisms of these energetic particles remain an open question. Possible candidates responsible for the acceleration have been put forward, such as Fermi acceleration, electron firehose, and lower hybrid drift instabilities and magnetic reconnection. However, to date, magnetic reconnection is only found in hybrid simulations during the generation of foreshock transients, but never reported by in situ observations. In this paper, we report an ion-scale flux rope observed at the trailing edge of a hot flow anomaly, which could be generated during the magnetic reconnection. Our observations indicate that reconnection could occur locally within foreshock transients and contribute to their particle acceleration.