Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere

We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics

Large-scale current systems and ground magnetic disturbance during deep substorm injections

We present a detailed analysis of the large-scale current systems and their effects on the ground magnetic field disturbance for an idealized substorm event simulated with the equilibrium version of the Rice Convection Model. The objective of this study is to evaluate how well the bubble-injection picture can account for some classic features of the substorm expansion phase. The entropy depletion inside the bubble is intentionally designed to be so severe that it can penetrate deep into geosynchronous orbit. The results are summarized as follows: (1) Both the region-1-sense and region-2-sense field-aligned currents (FACs) intensify substantially. The former resembles the substorm current wedge and flows along the eastern and western edges of the bubble. The latter is connected to the enhanced partial ring current in the magnetosphere associated with a dipolarization front earthward of the bubble. In the ionosphere, these two pairs of FACs are mostly interconnected via Pedersen currents. (2) The horizontal ionospheric currents show a significant westward electrojet peaked at the equatorward edge of the footprint of the bubble. The estimated ground magnetic disturbance is consistent with the typical features at various locations relative to the center of the westward electrojet. (3) A prominent Harang-reversal-like boundary is seen in both ground DH disturbance and plasma flow pattern, appearing in the westward portion of the equatorward edge of the bubble footprint, with a latitudinal extent of 5 and a longitudinal extent of the half width of the bubble. (4) The dramatic dipolarization inside the bubble causes the ionospheric map of the inner plasma sheet to exhibit a bulge-like structure, which may be related to auroral poleward expansion. (5) The remarkable appearance of the westward electrojet, Harang-reversal-like boundary and poleward expansion starts when the bubble reaches the magnetic transition region from tail-like to dipole-like configuration. We also estimate the horizontal and vertical currents using magnetograms at tens of ground stations for a deep injection substorm event occurred on April 9, 2008, resulting in a picture that is qualitatively consistent with the simulation. Based on the simulations and the observations, an overall picture of the ionospheric dynamics and its magnetospheric drivers during deep bubble injections is obtained

Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere

We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics

Simulated magnetopause losses and Van Allen Probe flux dropouts

Three radiation belt flux dropout events seen by the Relativistic Electron Proton Telescope soon after launch of the Van Allen Probes in 2012 (Baker et al., 2013a) have been simulated using the Lyon-Fedder-Mobarry MHD code coupled to the Rice Convection Model, driven by measured upstream solar wind parameters. MHD results show inward motion of the magnetopause for each event, along with enhanced ULF wave power affecting radial transport. Test particle simulations of electron response on 8 October, prior to the strong flux enhancement on 9 October, provide evidence for loss due to magnetopause shadowing, both in energy and pitch angle dependence. Severe plasmapause erosion occurred during ~ 14 h of strongly southward interplanetary magnetic field Bz beginning 8 October coincident with the inner boundary of outer zone depletion