Dependence of Mercurys magnetopause reconnection on the upstream conditions: 3D Hall-MHD simulations
Abstract
Observations from NASAs MESSENGER spacecraft reveal that Mercury has a miniature magnetosphere arising from the interaction of its intrinsic dipole field with the inner heliosphere solar wind. Compared to the terrestrial magnetosphere, Mercurys magnetosphere appears to be more dynamic in that the global timescales for plasma and magnetic flux circulation are much shorter, and the dayside magnetopause reconnection occurs at higher rates and under a wider range of magnetic shear angles. As a product of multiple X-line reconnection, flux transfer events (FTEs) are found to arise much more frequently with an occurrence rate of about 50 times higher than that detected at Earth. MESSENGER observations suggest that the different upstream solar wind conditions are likely the cause for large differences in reconnection-driven dynamics between Mercurys magnetosphere and Earths. In order to understand how reconnection rate and the characteristics of resultant FTEs vary with the upstream conditions, we have employed the BATSRUS Hall-MHD model with a high-resolution grid to simulate Mercurys magnetopause dynamics under a wide range of upstream solar wind and IMF conditions. Flux ropes are found to form due to multiple X-line reconnection in all our time-dependent Hall MHD simulations under fixed wind conditions, but their properties, such as occurrence rate and spatial scale, vary depending on the upstream parameters. We have developed automated techniques to identify and analyze FTEs in our simulations. The results of our analyses are compared directly with MESSENGER observations (e.g., Sun et al. 2020) and the comparison yields generally good agreement in terms of FTE spatial size, occurrence frequency, flux content, etc. The carefully designed Hall-MHD simulations allow us to examine how the properties of FTEs depend on parameters such as the solar wind Alfvenic Mach number, IMF orientation, and the magnetosheath plasma . With the global model, we also evaluate the global reconnection rate and the contribution of FTEs to the global circulation of magnetic flux at Mercury and how these properties vary in response to changes in the external conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.P24B..03L