Magnetic reconnection in the Earth's magnetosphere

为了理解磁尾动力学，确定在亚暴期间近地等离子体片中发生磁重联的位置是至关重要的。Geotail宇宙飞船在1995-2003年间在10-31 Re的径向距离上对近地磁尾进行了彻底的观测。利用强电子加速判据，确定了34个明显的重联事件。为了确定控制磁尾中磁重联位置的因素，研究了每次重联事件发生前的各种太阳风参数。对快速尾流事件进行了同样的分析。确定最重要的因素是太阳风的能量输入，可以用-Vx x b表示，其中Vx为太阳风速度的x分量，b为行星际磁场的南向分量。很可能是更高的能量输入，而不是总能量输入，主要控制磁重联的位置；当输入能量较高时，磁重联发生在离地球较近的地方。对不同编码下的磁重联进行了大量仿真。结果表明，只有当电流片厚度小于离子惯性长度时，才能快速触发磁重联。一般自发形成多个X线，多个X线并存发展。在磁重联的发展阶段，电子双流不稳定性提供了电子加速和混合。电子双流不稳定性的非线性相位产生静电孤立波（ESWs），这是航天器Geotail经常观测到的。

To understand magnetotail dynamics, it is essential to determine where magnetic reconnection takes place in the near-Earth plasma sheet during substorms. The Geotail spacecraft thoroughly surveyed the near-Earth magnetotail at radial distances of 10-31 Re during the years 1995-2003. Thirty-four clear reconnection events were identified using the criterion of strong electron acceleration. Various solar wind parameters prior to each reconnection events were examined in order to fine the factor controlling the location of the magnetic reconnection site in the magnetotail. The same analyses were carried out for fast tailward flow events. The most important factor was determined to be the solar wind energy input, which can be expressed by -Vx x Bs, where Vx is the x component of the solar wind velocity and Bs is the southward component of the interplanetary magnetic field. It is likely that higher energy input, rather than the total amount of energy input, primarily controls the location of magnetic reconnection; magnetic reconnection takes place closer to the Earth when the input energy is higher. A large number of simulations for magnetic reconnection in different codes were carried out. It is demonstrated that magnetic reconnection is quickly triggered only under the current sheet thickness smaller than ion inertial length. A multiple X lines commonly form spontaneously, and several X lines coexist and develop. In the developing phase of magnetic reconnection, electron two-stream instability provides electron acceleration and mixing. The nonlinear phase of the electron two-stream instability produces electrostatic solitary waves (ESWs), which are frequently observed by the spacecraft Geotail.