Detection of Magnetic Nulls around Reconnection Fronts

Abstract

Magnetic nulls, where magnetic-field strength becomes zero, play a crucial role in energy conversion and particle acceleration during magnetic reconnection. Recent simulations have suggested that reconnection fronts (RFs) inside the reconnection jet can host magnetic nulls. However, observational evidence for the RF-associated magnetic nulls remains absent so far. In this study, we present such evidence by using the first-order Taylor expansion method and Cluster measurements. We confirm for the first time the existence of magnetic nulls around RFs, and find that the dip region ahead of RFs and the nearby magnetic flux ropes around RFs can be host to magnetic nulls. The observed magnetic nulls are all spiral types, and the reconstructed topologies are consistent with theoretical models. Our results verify the existence of magnetic nulls around RFs, and may shed new light on the study of magnetic reconnection and RF dynamics.