Browsing by Subject "Geomagnetic storms"
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Item The Double Beltrami model of coronal mass ejections(2007-08) Kagan, Daniel Ross; Kumar, Pawan; Mahajan, Swadesh M.Coronal mass ejections (CMEs) are the most powerful events on the Sun and have important effects on Earth (geomagnetic storms), but their initiation is still not well understood. I show that the general class of Double Beltrami states, which are the lowest energy equilibria of Hall magnetohydrodynamics, can have characteristics similar to those of CME source regions in the solar corona and are capable of undergoing a catastrophe that can supply enough kinetic energy to create a CME. I then compare this Double Beltrami model of CMEs with observations. First, I show that the qualitative evolution of the DB state is consistent with that of a CME. Second, I carry out a detailed quantitative study of the expansion of the field during the quasi-equilibrium stage leading up to the catastrophe using LASCO C1 CME data, confirming the model prediction of an expansion of a factor of 1-2 in the height of the CME leading edge before major acceleration begins. Finally, I use the assumption that DB states are randomly chosen from the allowed phase space of coronal structures to predict the CME rate from the rate at which DB states appear. Taking each active region as having a corresponding DB state and using observational constraints to estimate that the state is replaced every 60 minutes by emerging loops results in a CME rate of 19.5 per day, which is in reasonable agreement with the actual rate of 6 per day at solar maximum (systematic uncertainties may be responsible for the differences that do exist). Future work for the dissertation will involve improvements leading up to a full simulation of the DB model including heat transfer, and the application of the model to stars and accretion disks.Item The study of interplanetary shocks, geomagnetic storms, and substorms with the WINDMI model(2009-08) Mays, Mona Leila; Horton, C. W. (Claude Wendell), 1942-WINDMI is a low dimensional plasma physics-based model of the coupled magnetosphere-ionosphere system. The nonlinear system of ordinary differential equations describes the energy balance between the basic nightside components of the system using the solar wind driving voltage as input. Of the eight dynamical variables determined by the model, the region 1 field aligned current and ring current energy is compared to the westward auroral electrojet AL index and equatorial geomagnetic disturbance storm time Dst index. The WINDMI model is used to analyze the magnetosphere-ionosphere system during major geomagnetic storms and substorms which are community campaign events. Numerical experiments using the WINDMI model are also used to assess the question of how much interplanetary shock events contribute to the geoeffectiveness of solar wind drivers. For two major geomagnetic storm intervals, it is found that the magnetic field compressional jump is important to producing the changes in the AL index. Further, the WINDMI model is implemented to compute model AL and Dst predictions every ten minutes using real-time solar wind data from the ACE satellite as input. Real-Time WINDMI has been capturing substorm and storm activity, as characterized by the AL and Dst indices, reliably since February 2006 and is validated by comparison with ground-based measurements of the indices. Model results are compared for three different candidate input solar wind driving voltage formulas. Modeling of the Dst index is further developed to include the additional physical processes of tail current increases and sudden commencement. A new model, based on WINDMI, is developed using the dayside magnetopause and magnetosphere current systems to model the magnetopause boundary motion and the dayside region 1 field aligned current which is comparable to the auroral upper AU index.