Investigations of Magnetic Reconnection at the Dayside Magnetopause

Magnetic reconnection at Earth's dayside magnetopause has traditionally been very difficult to analyze due the difficulty in locating where reconnection occurs for oblique IMF. However, new techniques make this possible by identifying magnetic separators, the curves that separate four regions of differing magnetic topology, and map the reconnection X-line. In this talk, we will discuss different methods for locating magnetic separators and apply them to 3-D resistive MHD simulations of the Earth's magnetosphere using the Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme code, although the methods described here are extensible to any global magnetospheric simulation model. Once the magnetic separators are found, one can calculate the electric field parallel to the separator and compare these results with a simple model of local two-dimensional asymmetric reconnection. To do so, plasma parameters that locally drive reconnection are measured in the magnetosheath and magnetosphere in planes perpendicular to the separator. We find that the predicted local reconnection rates scale well with the measured values in the simulations for oblique IMF with and without a dipole tilt. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. Finally, we compare separators in global simulations with MMS observations and find that separators are consistent with observed reconnection signatures.