MHD simulations of magnetospheric response to strong solar wind driving: Polar cap potential saturation

The coupling of the solar wind with the magnetosphere and ionosphere controls the geomagnetic activity in our environment. Knowing how this coupling takes place is of particular interest to space physics and has significant consequences on space weather. Observations have shown that this coupling during strong driving is not a linear phenomenon; during such extreme conditions there is a feedback effect from the ionosphere that changes the coupling between the solar wind and the magnetosphere. Different models, empirical and physical, have attempted to explain this behavior and although advances on its understanding have been made, a definite answer is not available yet. In this study, we present a different comprehensive model of this coupling based on the global Lyon-Fedder-Mobarry magneto-hydrodynamic code of the magnetosphere and ionosphere. This model incorporates the role of the bow shock during strong driving and recognizes its function in the coupling mechanism. This dissertation shows that during saturation, the current flowing in the bow shock dissipates a significant fraction of the dynamic pressure of the solar wind, and since this current closes with Region1 type currents flowing in open field lines from the ionosphere, the ionospheric convection is no longer controlled by dayside reconnection but by the current required to closed the bow shock current. We used idealized solar wind conditions to parameterize the role of conductance, dynamic pressure and solar wind configuration on this model. Also, evidence of FACs flowing in open flux regions is provided using DMSP spacecraft data. These currents are required and suggested not only by the saturation mechanism introduced in this work but also by previous studies of polar cap potential saturation. Finally, a case study of the "Halloween storm of 2003" is presented to test the comprehensive model.