Conditions for drastic evolution of magnetospheric current wedge

Recently, it was demonstrated that magnetospheric current wedge drastically builds up as soon as the fast reconnection mechanism is triggered to cause three-dimensional magnetic field dipolarization in a finite extent in the east-west direction. The present paper further studies the current wedge dynamics for different values of k z , taken as a parameter, which specifies the effective east-west extent, inside which magnetic reconnection proceeds. It is demonstrated that only when the east-west width of the initial current sheet becomes 3–4 times larger than its thickness, the current wedge is allowed to drastically evolve; otherwise, no current wedge can occur. For the critical case, the temporal dynamics of fast reconnection and the associated current wedge evolution become more unsteady or impulsive; in particular, when the fast reconnection jet collides with the expanding magnetic loop, the sheet current, located at a considerable distance from the loop top, abruptly turns its direction to form a large-scale current wedge.