Guide-Field Dependence of Dissipation Processes in Magnetopause Reconnection

Magnetospheric Multiscale (MMS) has encountered several reconnection dissipation regions in the vicinity of magnetic nulls (X-lines) and flow stagnation points for asymmetric reconnection at the Earth's magnetopause. To date two high-shear reconnection events and two moderate guide-field events have been analyzed for characteristic currents, electron distribution functions, vector electric fields and waves. The goal is to determine the guide-field dependence of the sources of reconnection electric fields, the locations of energy conversion as determined by J dot (E + v x B)>0, the current-carrying features of the distribution functions (non-gyrotropic or field-aligned) and turbulence and associated wave modes (whistler, upper hybrid, lower-hybrid, etc.) that are generated near the dissipation region. This work builds on two published studies that showed for a high-shear reconnection event that the dissipation was localized to the flow stagnation point while for a guide-field of 1 dissipation occurred at both the magnetic null and the flow stagnation point with a quiescent region in between. The out-of-plane currents were carried by field-aligned beams along the guide field at the magnetic null while for both types of events the out-of-plane currents were carried by non-gyrotropic (crescent) distributions at the flow stagnation point. The research reported here builds upon these results by analyzing the sources of the reconnection electric field, which were predicted by modeling to be electron inertia at the magnetic null and divergence of electron pressure tensor at the flow stagnation point. In addition, electromagnetic waves and turbulent plasma oscillations within and near the dissipation regions are compared for the four events.