磁场重联耗散区内X线附近的强低混杂波的Geotail卫星观测研究

Intense lower hybrid waves within the reconnection diffusion region near X-line by Geotail observation

Geotail卫星于2003年5月15日在近地磁尾观测到磁场重联并穿越重联耗散区.卫星从尾向—南尾瓣一侧穿越磁场重联耗散区到地向—北尾瓣一侧的过程中,随着等离子体流反向,霍尔磁场(By)被观测到.本文研究了该磁场重联耗散区内的低混杂波.观测结果显示,在磁场重联耗散区核心及其附近区域观测到在低混杂频率附近存在强烈的等离子体波动的增强,其传播方向主要垂直于背景磁场,该等离子体波动为低混杂波.前人的模拟结果认为,当磁场重联得到充分发展之前,低混杂波将消失.本文的观测结果充分说明,当磁场重联充分发展之后,在核心区域仍然存在增强的低混杂波,说明低混杂波贯穿磁场重联的整个发展过程.这种观测结果与计算机等离子体模拟的结果有所不同.本文的观测对低混杂波在磁场重联中的具体表现提供了新的观测证据并有可能修正前人的理论.

The Lower Hybrid Wave （LHW） is studied within magnetic reconnection diffusion region in the near-earth tail by Geotail on May 15, 2003. The Hall magnetic field （By） is observed when plasma flow reverses during the Geotail crossing the reconnection diffusion region from tailward-southern-lobe side to earthward-northern-lobe side. Intense waves enhancement near lower hybrid frequency （fLH≈6. 8 Hz） is observed both within and around the reconnection diffusion region with the propagation vector mainly perpendicular to the ambient field and they are identified as LHW. The observation of LHW near the reconnection X-line suggests that the LHW is still active after the magnetic reconnection has been triggered and developed into matured X-line. This result is different with the simulation which suggested that LHW disappears as soon as an X-line is matured. Our observation will shed new light on the understanding of the role and behavior of the LHW in the magnetic reconnection developing process.