IMF北向时太阳风粒子向磁层输运的试验粒子模拟研究

Test Particle Simulation of Solar Wind Transport into the Magnetosphere during Northward IMF

以ACE卫星实时观测数据驱动的全球磁流体模拟为背景场,选取2003年10月22-24日行星际磁场(IMF)持续北向的事件,使用试验粒子方法,对太阳风粒子向磁层输运的过程进行模拟研究,分析北向IMF下太阳风粒子注入磁层过程中粒子在磁层内的空间分布和时间演化特征。IMF北向期间,进入环电流区域的粒子在晨侧区域的密度大于昏侧,且晨侧的粒子分布范围更广。背阳面磁鞘中的太阳风粒子可以通过低纬边界层进入磁层,但很难通过南北侧磁层顶进入磁层。进入磁尾的太阳风粒子聚集形成冷而密的等离子体片(CDPS),模拟中CDPS的空间分布和密度大小与观测数据符合。在IMF长时间北向期间,磁尾的粒子数量呈现随时间增长的趋势,并存在约20 min的小幅度准周期变化和约5~6 h的较大幅度的准周期变化。

Using test particle method,with the background fields obtained from a global Magnetohydrodynamics(MHD)simulation driven by the ACE satellite observation data,the transport process of solar wind particles into the Earth’s magnetosphere was simulated during a long-term northward Interplanetary Magnetic Field(IMF)event on 22-24 October 2003.The particle density distribution in the magnetosphere and the time evolution characteristics of the particles were analyzed and discussed.During the northward IMF,the particle density in the dawn-side ring current region is higher than that on the dusk side,and the radial range on the dawn side is wider.The magnetosheath particles on the tail side can transport into magnetosphere through the low-latitude boundary layer,but they are difficult to enter into magnetosphere through the north and south magnetopause.The solar wind particles transported into the nightside magnetosphere gather to form a Cold Dense Plasma Sheet(CDPS).The spatial scale and particle density of the CDPS obtained from the simulation are consistent with observations.During the long-term northward IMF period,the total number of particles in the magnetotail showed a trend of increasing over time.At the same time,there exists a weak quasi-periodic variation with a period of about 20 min and a strong quasi-periodic variation with a period of about 5~6 h.