An initial investigation of the magnetosphere at a system level using auroral oval radius and ring current intensity as state variables

One approach to understanding the magnetosphere at a system level is to select a number of magnetospheric state variables and to examine statistically their inter-relationships and the temporal evolution of the magnetosphere through state-space. This talk outlines a first attempt at such a study, using the radius of the auroral oval, a proxy for the open flux content of the magnetosphere, and the Sym-H index, a measure of the intensity of the ring current, as the primary state variables. Using observations from the two-year period June 2000 to May 2002, the response of the state of the magnetosphere to differing solar wind inputs, and the evolution of the system state during geomagnetic storms is investigated. Our main finding is a characteristic evolution of magnetospheric state through the initial, main, and recovery phases of geomagnetic storms. We discuss our findings within the context of the expanding/contracting polar cap paradigm, in terms of a modification of substorm onset conditions by the magnetic perturbation associated with the ring current.