Global magnetohydrodynamic simulations of resonant ultra-low frequency mode coupling in the inner magnetosphere and plasmasphere

Global-scale, three-dimensional simulations of the solar wind/magnetosphere/ionosphere interaction have reached a level of sophistication that permits a consideration of resonant ultra- ow frequency (ULF) waves in a realistic magnetospheric configuration. In particular, recent work has successfully coupled the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model and the Rice Convection Model (RCM). The coupled LFM-RCM model allows, for the first time, a study of resonant ULF mode coupling in a global- scale, 3D simulation that includes a plasmasphere. We explore the role that solar wind dynamic pressure fluctuations play in the generation of magnetospheric ULF waves, using idealized solar wind configurations to drive the simulations. We present results from both the stand-alone LFM (no plasmasphere) and the coupled LFM-RCM (with plasmasphere), with identical boundary conditions in both simulations. In this numerical experiment, we impose both monochromatic and quasi-broadband ULF fluctuations (~0-30 mHz) in solar wind dynamic pressure on the magnetosphere. We find toroidal mode field line resonances (FLRs) and cavity/waveguide modes in the magnetospheric response, consistent with well-established mode coupling theory. The inclusion of the plasmasphere in the global simulation has a profound effect on the resonant ULF modes generated. Accurately modeling resonant ULF waves is critical for radial diffusion based models of the Eath's radiation belts, and thus for modeling inner magnetospheric dynamics, in general. To the best of our knowledge, these results are the first to explicitly and unambiguously reproduce such inner magnetospheric resonances using a global simulation of the solar wind/magnetosphere/ionosphere interaction.