Browsing by Author "Pembroke, Asher"

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    A Dynamic Coupled Magnetosphere-Ionosphere-Ring Current Model
    (2013-09-16) Pembroke, Asher; Toffoletto, Frank R.; Warren, Joe; Reiff, Patricia H.
    In this thesis we describe a coupled model of Earth's magnetosphere that consists of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamics (MHD) simulation, the MIX ionosphere solver and the Rice Convection Model (RCM). We report some results of the coupled model using idealized inputs and model parameters. The algorithmic and physical components of the model are described, including the transfer of magnetic field information and plasma boundary conditions to the RCM and the return of ring current plasma properties to the LFM. Crucial aspects of the coupling include the restriction of RCM to regions where field-line averaged plasma-beta <=1, the use of a plasmasphere model, and the MIX ionosphere model. Compared to stand-alone MHD, the coupled model produces a substantial increase in ring current pressure and reduction of the magnetic field near the Earth. In the ionosphere, stronger region-1 and region-2 Birkeland currents are seen in the coupled model but with no significant change in the cross polar cap potential drop, while the region-2 currents shielded the low-latitude convection potential. In addition, oscillations in the magnetic field are produced at geosynchronous orbit with the coupled code. The diagnostics of entropy and mass content indicate that these oscillations are associated with low-entropy flow channels moving in from the tail and may be related to bursty bulk flows and bubbles seen in observations. As with most complex numerical models, there is the ongoing challenge of untangling numerical artifacts and physics, and we find that while there is still much room for improvement, the results presented here are encouraging. Finally, we introduce several new methods for magnetospheric visualization and analysis, including a fluid-spatial volume for RCM and a field-aligned analysis mesh for the LFM. The latter allows us to construct novel visualizations of flux tubes, drift surfaces, topological boundaries, and bursty-bulk flows.
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    LFM-RCM: Toward a coupled description of the inner and outer magnetosphere
    (2009) Pembroke, Asher; Toffoletto, Frank
    Numerical simulations of magnetohydrodynamics (MHD) have led to reasonable descriptions of the general morphology and dynamics of Earth's magnetosphere. However, MHD is invalid in regions close to the Earth where gradient and curvature drifts are comparable to the E × B drift. The Rice Convection Model was designed to take into account such dynamics and provide a more realistic description of the plasma distribution, using an input magnetic field model such as the Lyon Fedder Mobarry (LFM). Recent efforts to couple the RCM and the LFM have led to a more complete picture of magnetospheric processes. This thesis describes the physics of the two regions, our coupling paradigm, and analysis tools for interpreting these results.