Magnetic Nulls in the Reconnection Driven by Turbulence

Abstract

Abstract For the first time, we use spacecraft measurements to investigate the magnetic nulls in a reconnection event driven by turbulence in the magnetosheath. We particularly focus on the relation between magnetic-null topologies and currents, which can be decomposed into a component perpendicular to spine ( ) and a component parallel to spine ( ). Our new observations include: (1) the total current at spiral nulls is much larger than that at radial nulls; (2) is large at spiral nulls but small at radial nulls; (3) at radial nulls, is dominant, while at spiral nulls, is dominant; (4) the fan-spine angle θ at both radial and spiral nulls decreases with , with a clear upper boundary; (5) with a database of 715 nulls, we statistically resolve the relation between θ and as with the correlation coefficient of cc = 0.71 (radial null) and with cc = 0.76 (spiral null), where is in the unit of . Our physical interpretations of these observations are: (1) the current parallel to spine significantly determines the null topology, with large producing spiral nulls and small producing radial nulls; (2) the current perpendicular to spine serves to tilt the fan plane to the spine, for both spiral and radial nulls. All of these observations and conclusions significantly improve our understanding of magnetic reconnection.