Hybrid and Hall‐MHD simulations of collisionless reconnection: Dynamics of the electron pressure tensor

In this study we compare the results of two‐dimensional hybrid (particle ions, massless fluid electrons) and Hall‐MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. As in the recent Geospace Environment Modeling (GEM) reconnection challenge studies, we find overall agreement between the two calculations in both the reconnection rate and the global configuration. Results of this study show that in addition to providing the reconnection electric field at the X point the divergence of the electron pressure tensor leads to in‐plane electric fields that exert drag forces on the ions as they enter and exit the near‐X‐point region. The in‐plane electric fields are enhanced in regions of small transverse scale along the edge of the sheet, and the resulting narrow electron current layers are demonstrated clearly. The possibility of improving magnetotail reconnection models by embedding a Hall‐MHD calculation using the electron pressure tensor model inside a large‐scale MHD simulation is suggested.