Solar Wind Energy Transfer to Geospace during Periods with Large Transverse Interplanetary Magnetic Field (IMF)

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The major factor in the solar wind that controls magnetospheric activity is the direction and magnitude of the interplanetary magnetic field (IMF). When the IMF is relatively small, and the mach number of the solar wind flow is large, the magnetosphere responds linearly to changes in the solar wind driver. In particular, the ionospheric potential across the polar cap (which regulates ionospheric and magnetospheric plasma convection) is linearly related to the solar wind electric field for southward IMF. However, when the IMF is large, the magnetospheric response is non-linear, and the polar cap potential saturates with respect to the solar wind electric field. This project will investigate this non-linear response of the magnetosphere through the use of global magnetohydrodynamic (MHD) simulations of the solar wind interacting with the magnetosphere. Simulations results will be verified using data sets from various spacecraft missions and ground-based observations. The aim of the research is to answer the question "What is the fundamental physics that produces a nonlinear magnetospheric response to large values of the Interplanetary Magnetic Field (IMF) and how does this manifest itself for various orientations of the IMF?" Preliminary work suggests that a crucial aspect of the underlying physics is the closure of the large current produced at the bow shock and the dominance of magnetic forces over plasma pressure gradients in determining the solar wind flow around the magnetosphere and the interaction of the solar wind with the magnetosphere during periods of low magnetosonic Mach number flow. The closure of the dynamo bow shock current through the ionospheric load may provide a means of directly transferring solar wind mechanical energy extracted from the flow at the bow shock to the ionosphere on open field lines. Such a mechanism is physically distinct from both magnetic reconnection and the viscous interaction, and represents a third, fundamental mode of transferring solar wind energy to the geospace system. This projects suggests a new and potentially transformative paradigm for solar wind energy transfer to the geospace system that not only would be able to explain a range of nonlinear magnetospheric responses to large IMF values, but also would provide a framework for the reinterpretation of known, but not well understood phenomena such as lobe cell convection and interhemispheric asymmetries. The project includes support and training for a graduate student through the Ph.D. In addition, several undergraduate students will be involved, including minority students. All students will give presentations at meetings and be involved in publication of the results. Results of the research will be presented to the general public through visualizations at the University of Texas, Arlington Planetarium.