Correlations of Plasma Properties Between the Upstream Magnetosheath and the Downstream Outflow Region of Magnetopause Reconnection

The impact of upstream conditions on magnetopause reconnection has been an intriguing question in solar wind-magnetosphere coupling. In this study, we conduct a statistical analysis of plasma properties in the reconnection outflow region and the associated upstream solar wind/magnetosheath. We observe that the normalized ion density (N/Nsw) decreases and the flow speed (V/Vsw) increases in the upstream magnetosheath with distance from the subsolar point, consistent with previous models and observations. The magnetic field strength (|B|), ion density (N), and ion bulk speed (|V|) in the upstream magnetosheath exhibit close correlations with those in the reconnection outflow region. This upstream-downstream correlation likely arises from the process of forming reconnection outflows, where most upstream ions cross the separatrix and mix with ion outflow already accelerated near the X-line. High-speed part of reconnection outflow is mostly located on the magnetosphere side of the magnetopause current layer, with outflow velocities peaking close to the upstream magnetosheath Alfv & eacute;n speed. The spatial extent of high-speed outflow is greater in conditions of lower solar wind Alfv & eacute;n Mach number (MA,sw). Additionally, the southward magnetic field in the magnetosheath and |B| of magnetopause current layer are larger in the cases of lower MA,sw. These findings indicate a close connection of plasma properties between the outflow region of magnetopause reconnection and the upstream magnetosheath. Plasma and magnetic fields in the upstream magnetosheath/solar wind correlate with those in the outflow region of magnetopause reconnection In the upstream magnetosheath and the outflow region, ion density decreases and flow speed increases with distance from the subsolar point The spatial extent of reconnection outflow in the magnetopause current layer is larger at lower solar wind Mach numbers