Simultaneous Observation of the Inner and Outer Electron Diffusion Region in Reconnection with Large Guide Field

Abstract

Abstract This paper presents a simultaneous observation of the inner and outer electron diffusion region (EDR) at the dayside magnetopause by the magnetospheric multiscale (MMS) spacecraft. The EDR was observed in magnetic reconnection with a large guide field. The inner EDR was characterized by positive J · E ′ while the outer EDR is manifested by negative J · E ′ and opposite out-of-plane electric field to that in the inner EDR. One pair of the spacecraft detected the inner EDR while the other pair encountered the outer EDR. Moreover, the two pairs were on the opposite side of the X-line as they observed the bidirectional accelerated electron jets. The fortuitous formation of MMS allows us to estimate the maximum length of the inner EDR as ∼36 d e and the lower bound of the reconnection rate as 0.142 ± 0.041. These observations have far-reaching implications for understanding the electron physics in reconnection.