Parametric Exploration of Magnetic Reconnection at the Bow Shock: Hybrid Simulations
Presentation Type
Talk
Presenter Format
Virtual Meeting Talk
Topic
Dayside Science
Start Date
10-5-2022 10:45 AM
Abstract
Recent observations by Magnetospheric Multiscale (MMS) have demonstrated that magnetic reconnection occurs at Earth’s bow shock, typically at thin current sheets arising from plasma instabilities and turbulence in the shock transition region. Broad observational surveys of both the shock transition region and the magnetosheath downstream suggest that the number of thin current sheets in these regions is not strongly dependent on the shock Mach number or the angle between the upstream magnetic field and shock normal (θBn). This result is somewhat surprising given that quasi-parallel and high Mach number shocks tend to have more disordered and non-stationary structure. In order to investigate how shock reconnection manifests across different parameters, we perform a series of hybrid (fluid electron, kinetic ion) particle-in-cell simulations across a broad range of Mach numbers and orientations. Given that hybrid simulations cannot resolve electron-scale reconnection, these simulations isolate a ‘long-wavelength’ mechanism for shock reconnection driven by unstable waves in the upstream foot region. We find that this mechanism is strongly constrained to quasi-parallel shocks across all simulated Mach numbers. Furthermore, the number of reconnecting structures and closed-field volume increases with Mach number and decreases with θBn in the upstream and ramp regions. Downstream of the shock, however, we find a similar result to observational surveys: within the sub-population of quasi-parallel shocks, the number and decay rate of reconnecting structures are not strongly dependent on upstream shock parameters.
Parametric Exploration of Magnetic Reconnection at the Bow Shock: Hybrid Simulations
Recent observations by Magnetospheric Multiscale (MMS) have demonstrated that magnetic reconnection occurs at Earth’s bow shock, typically at thin current sheets arising from plasma instabilities and turbulence in the shock transition region. Broad observational surveys of both the shock transition region and the magnetosheath downstream suggest that the number of thin current sheets in these regions is not strongly dependent on the shock Mach number or the angle between the upstream magnetic field and shock normal (θBn). This result is somewhat surprising given that quasi-parallel and high Mach number shocks tend to have more disordered and non-stationary structure. In order to investigate how shock reconnection manifests across different parameters, we perform a series of hybrid (fluid electron, kinetic ion) particle-in-cell simulations across a broad range of Mach numbers and orientations. Given that hybrid simulations cannot resolve electron-scale reconnection, these simulations isolate a ‘long-wavelength’ mechanism for shock reconnection driven by unstable waves in the upstream foot region. We find that this mechanism is strongly constrained to quasi-parallel shocks across all simulated Mach numbers. Furthermore, the number of reconnecting structures and closed-field volume increases with Mach number and decreases with θBn in the upstream and ramp regions. Downstream of the shock, however, we find a similar result to observational surveys: within the sub-population of quasi-parallel shocks, the number and decay rate of reconnecting structures are not strongly dependent on upstream shock parameters.
