Reconnection guide field and quadrupolar structure observed by MMS on 16 October 2015 at 1307 UT

Abstract

We estimate the guide field near the X point, BM0, for a magnetopause crossing by the Magnetospheric Multiscale (MMS) spacecraft at 1307 UT on 16 October 2015 that showed features of electron-scale reconnection. This component of the magnetic field is normal to the reconnection plane L-N containing the reconnection magnetic field, BL, and the direction eN normal to the current sheet. The BM field component appears to approximately have quadrupolar structure close to the X point. Using several different methods to estimate values of the guide field near the X point, some of which use an assumed quadrupolar symmetry, we find values ranging between −3.1 nT and −1.2 nT, with a nominal value of about −2.5 nT. The rough consistency of these values is evidence that the quadrupolar structure exists.