Browsing by Author "Ding, Cheng"

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    Analytical and numerical modeling of the electromagnetic structure of geospace
    (1995) Ding, Cheng; Hill, Thomas W.
    Geospace is a vast complex system. A portable quantitative model of the geospace electromagnetic structure is the foundation of many researches in the area of space plasma physics. Work described in this dissertation uses both the analytical and numerical approaches to bring the existing models several steps closer to the ultimate model. An analytical model is developed to simulate the magnetic effect of the magnetopause current by solving the Laplace equation in a complex geometry. The procedure involves the minimization of an integral quantity to determine the coefficients of a harmonic expansion for the magnetic scalar potential of the magnetopause field. This procedure can shield any kind of interior magnetic field, or open the closed magnetosphere up with an arbitrary normal component distribution over the magnetopause. The Toffoletto and Hill 1993 open magnetosphere model is improved by adding a new physical module of the shielded ring current field, and modifying its additional tail field to eliminate the shortcomings that are evident. The new improved version has a better representation of the magnetic field in the inner magnetosphere. A numerical model for the electric potential on closed field lines is developed by extending the polar-cap potential into the low-latitude ionosphere using a finite element method. This significantly enhances the model's capability. By mapping the electric potential into the magnetosphere, the associated magnetospheric plasma convection can be examined to assess the reasonability of the normal component distribution on the magnetopause.
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    Mapping magnetic flux tubes and field aligned currents using two representative magnetospheric models
    (1993) Ding, Cheng; Hill, Thomas W.
    Among available quantitative magnetospheric models, the Tsyganenko models represent empirical modeling, while the Toffoletto and Hill model is theoretical analysis. By mapping flux tubes between the ionosphere and the magnetosphere, those two models are analyzed and compared. Both the implied and actual field-aligned currents (FAC) are calculated in both models. The implied FAC, required to maintain the model field in magnetostatic equilibrium and given by the Vasyliunas equation, has the same order of magnitude as observational data, even in non-equilibrium models. The actual FAC, given by Ampere's law, is much smaller than the implied FAC, which means no large extraneous FAC is included in those models. Several new approaches imply that none of these models are in magnetostatic equilibrium, while the discrepancies are considerably larger for the Tsyganenko models. The magnetic effects of a preliminary FAC model have been evaluated in the Toffoletto and Hill theoretical model.