Reconstruction of the Asymmetric Magnetic Reconnection Region at the Magnetopause

Abstract:

Magnetic reconnection at the magnetopause is a key process coupling the earth’s magnetosphere with interplanetary space. Multiple spacecraft measurement makes it possible to study observationally the structure of the reconnection region. In this paper we improve the fitting-reconstructing method developed by He et al. [2008] and use it to investigate the asymmetric reconnection event observed by Cluster on Apr. 06, 2004. The reconnection site was encountered when the constellation traversed the dayside magnetopause at z~5.3Re, with spacecraft separations less than 400km. The reconstructing results clearly revealed the asymmetric geometry of the reconnection region. The orientation of the X-line, which was reproduced as the separator linking a pair of magnetic null points, was shown to be ~60° away from the M-direction in the local LMN coordinate. Bipolar and unipolar Hall fields were both seen by different spacecraft, implying that the reconnection regime was 3D in nature, and the difference in Hall fields could be related to the existence of two null points which restricted the length of the separator. In addition, electromagnetic lower hybrid waves are found to be enhanced on the magnetospheric side of the reconnection region. The reconstructing results are helpful for providing a 3D picture of the asymmetric reconnection region, and the improved reconstructing method can be applied to analyze the data from MMS which is deployed with small separations of satellites.