磁层顶的涡旋诱发重联和单X线重联

用二维MHD数值模拟研究了地球磁层顶的涡旋重联和单X线重联,并将两者作了比较。涡旋重联和单X线重联各在Alfvèn马赫数M_Λ大于和小于0.5时出现于向阳面磁层顶。前者所产生的磁岛与涡旋同心重叠;后者磁力线重联仅产生X点,而不闭合形成磁岛,涡旋分布于X点两侧。在涡旋重联的自组织过程中,互螺旋度等近似守恒决定其渐近态的拓扑结构。最后,讨论了这两种重联对通量传输事件所起的不同作用。

VORTEX-INDUCED RECONNECTION AND SINGLE X LINE RECONNECTION AT THE EARTH''''S MAGNETOPAUSE

Vortex-induced magnetic reconnection (VITM) and single X line magnetic reconnecfion (SXMR) at the dayside magnetopause are investigated by using two dimensional MHD simulation.It is found that VIMR and SXMR occur,respectively,when the flow-aligned Alfven Mach number is larger and smaller than ~0.5.The large scale magnetic island and flow vortex seen in the asymptotic state of VIMR are co-located and concentric,while for SXMR,the reconnected field lines do not form close loops,only an X point is produced with vortices appeared around the X point.Several ideal topological invariants,such as the mutuaJ hehory,etc.,play an essential role in determining the asymptotic patterns of physical fields in the self-organization process of VIMR.The relative importance of VIMR as compared with SXMR in yielding the magnetic flux transfer events at the dayside magnetopause are also discussed.