Simulating Extreme Space Weather With Kinetic Magnetotail Reconnection

Abstract Extreme space weather events require particle‐in‐cell (PIC) modeling to capture the kinetic physics of magnetic reconnection that is not present in magnetohydrodynamic (MHD) models. The MHD with Adaptively Embedded Particle‐In‐Cell (MHD‐AEPIC) model (Chen et al., 2020, https://doi.org/10.1029/2020ea001331 ) builds on the operational Michigan Geospace space weather model by coupling the FLexible Exascale Kinetic Simulator (FLEKS) PIC code (Chen et al., 2023, https://doi.org/10.1016/j.cpc.2023.108714 ). The adaptive coupling selects the active PIC domain based on local criteria that identify potential reconnection sites. This saves computational cost compared to large static PIC regions while including full kinetic physics where necessary. Here, the PIC code is activated to follow a flapping plasma sheet and adaptively select areas of potential reconnection. This eliminates the need to constantly cover a huge volume with PIC for the entire simulation timeframe. X. Wang et al. (2022a), https://doi.org/10.1029/2021ja030091 shows the advantages of MHD‐AEPIC in representing local particle distributions in the tail and producing global geomagnetic indices for a strong geomagnetic storm. We build on that work by applying the MHD‐AEPIC model to two extreme geomagnetic storms, the Halloween 2003 and the November 2003 events, to investigate the impact of a kinetic description of tail reconnection for extreme solar wind driving. Adding the PIC code causes dramatic changes in magnetotail magnetic topology and in global geomagnetic indices for these events when compared to ideal MHD. Our simulations with the MHD‐AEPIC model are robust under extreme driving conditions for both events, forming a foundation for exploring hypothetical driving conditions to assess the potential impacts of “worst‐case” storms.