Spatiotemporal activity of magnetic storms

We have constructed a data-derived model of the evolution of the spatial st ructure of the ring current geomagnetic signature during storms. A spatiall y dependent generalization of the Dessler-Parker-Skopke relation has been d erived to explain the spatial structure in the midlatitude magnetic fluctua tions (MLMF) as observed by ground magnetometers. Such a relation is used a s a basis for constructing solar-wind-driven, data-derived models of the ML MF. The model includes a coupling to the solar wind as the energy driver an d also includes a nonlocal coupling as an explanation of the inhomogeneity in the energy density that appears in the ring current during the main phas e of a storm. Both linear and nonlinear models for the evolution of the spa tial structure of the MLMF are constructed, and the nonlinear spatial model of the ring current produces better predictions than the linear one. This can be taken as an indication that during strong magnetic storms the ring c urrent evolves in a nonlinear fashion. The spatial data used in the generat ion of the models are rotated to a frame "fixed" with the ring current, and presure effects were accounted through a kinematic relation. The technique s developed in this paper are very general and can be used to study other s ystems that show spatial structure, such as the high-latitude current syste m.