Kinetic signatures, asymmetries, and FTEs associated with Mercury’s dayside magnetopause reconnection as revealed by 3D MHD-AEPIC simulations

Abstract

Mercury possesses a dynamic magnetosphere driven primarily by magnetic reconnection occurring regularly at the magnetopause and in the magnetotail. Using the Magnetohydrodynamics with Adaptively Embedded Particle-in-Cell (MHD-AEPIC) model, we have performed a series of global simulations with different upstream conditions to study in detail the kinetic signatures, asymmetries, and flux transfer events (FTEs) associated with Mercury’s dayside magnetopause reconnection. By treating both ions and electrons kinetically, the embedded PIC model reveals crescent-shaped phase-space distributions near reconnection sites, counter-streaming ion populations in the cusp region, and strong temperature anisotropies within FTEs. A novel algorithm has been developed to automatically identify reconnection sites in our 3D simulations. The spatial distribution of reconnection sites as modeled by the PIC code exhibits notable dawn-dusk asymmetries, likely due to such kinetic effects as X-line spreading and Hall effects. Across all simulations, simulated FTEs occur quasi-periodically every few seconds with their key properties showing clear dependencies on the upstream solar wind Alfvénic Mach number and the IMF orientation, consistent with MESSENGER observations and previous Hall-MHD simulations. FTEs formed in our MHD-AEPIC model are found to contribute a significant amount (~ 3% - 36%) of the total open flux generated at the dayside magnetopause. Taken together, the results from our MHD-AEPIC simulations provide new insights into the kinetic processes associated with Mercury’s magnetopause reconnection that should prove useful for interpreting in situ observations from MESSENGER and BepiColombo.