The investigators will use a global circulation model of the Earth's magnetosphere to study key aspects of substorms and their global consequences. The methodology is to use solar wind data as input to the simulation model and critically compare the results with observations in the magnetosphere and ionosphere. By combining simulation results with observational data, the investigators will overcome the limited spatial and temporal resolution of observations and be able to produce accurate, high resolution synoptic maps of the magnetosphere and ionosphere. With these maps the investigators will study key issues of substorm research, such as the detailed topology of substorm current systems and the timing of substorm signatures. The research will lead to a better understanding of geomagnetic activity and substorms and aid in the development of improved space weather predictions.