Large-scale Coupled Models of the Inner Magnetosphere
Doctor of Philosophy
In magnetospheric physics nowadays, the pursuit of realistic numerical simulation of the inner magnetospheric physics of plasma transport, ring current formation and storm-triggered Earth electromagnetic field changes is an ongoing challenge. To this end, we have implemented a large-scale coupled scheme of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model with the Rice convection model - equilibrium (RCM-E), the ring current model equipped with a magneto-friction (MF) solver, called LFM-RCM-E. The purpose of the one-way coupling scheme is to allow the RCM-E to continuously update its boundary conditions from the LFM while preserving entropy conservation. It enables a high-resolution self-consistent ring current model with realistic time-dependent outer-magnetospheric magnetic field configurations. Compared with the prior LFM-RCM, the LFM-RCM-E resolves the issue of a restricted simulation region due to a plasma - β constraint that is used to ensure numerical stability. By introducing the MF equilibrium solver, the RCM simulation region expands father out into the plasma sheet where the storm-time plasma transportation takes place. In the ionosphere, the RCM-E replaces the ionospheric electric field solver (MIX) of LFM with the one used by the RCM. The electric potential produced, along with the realistic ionospheric precipitation patterns shows strong consistency with the plasma motion featured with well resolved bubbles and bursty bulk flows. This thesis gives detailed descriptions of the coupling scheme of the model in Chapter 3. A test case of the model is shown in Chapter 4, where results of an idealized event simulation will be presented and discussed. Apart from an idealized event, a robust model should be able to simulate realistic severe space weather events. Chapter 5 presents its application in simulating a real event, the June 1st 2013 storm. The model is run with large solar wind ram pressure and tilted solar wind directions that impact the Earth magnetospheric system on the dayside. A routine of adaptive boundary decision is implemented to ensure a valid RCM simulation region and thus enhances the robustness of the model. Model - data comparisons are conducted, in terms of Dst index, plasma pressure and magnetic field, with Van Allen Probes data. The coupled scheme of LFM-RCM-E is applicable to other global MHD models. Chapter 6 presents the work of a collaborative project with the National Center for Atmospheric Research (NCAR), which is the implementation of a new branch of a coupled MHD code with the aim studying sub-aurora polarization streams (SAPS). Since the RCM ionospheric precipitations are a significant source of diffuse aurora and are responsible for the dynamic change of ionospheric conductivity, feedback channels from RCM to the Coupled Magnetosphere-Ionosphere-Thermosphere model (CMIT), have been established. The fully coupled CMIT-RCM, a.k.a., LFM-RCM-TIEGCM system will be an ideal tool to simulate and analyze SAPS phenomenon comprehensively. The electron average energy has always been underestimated by RCM due to a naïve cold plasmasphere model. Chapter 7 presents the work of integrating a more sophisticated plasmasphere model, modified from the global core plasma model (GCPM), into LFM-RCM-TIEGCM. The geometry of the plasmasphere depends on a measure of the geomagnetic activity, the Kp-index. A set of control experiments shows a substantial increase in the electron average energy and energy flux with the new plasmasphere model.