A DESCRIPTION OF THE SOLAR-WIND MAGNETOSPHERE COUPLING BASED ON NONLINEAR FILTERS

A nonlinear filtering method is introduced for the study of the solar wind - magnetosphere coupling and related to earlier linear techniques . The filters are derived from the magnetospheric state, a representat ion of the magnetospheric conditions in terms of a few global variable s, here the auroral electrojet indices. The filters also couple to the input, a representation of the solar wind variables, here the rectifi ed electric field. Filter-based iterative prediction of the indices ha s been obtained for up to 20 hours. The prediction is stable with resp ect to perturbations in the initial magnetospheric state; these decrea se exponentially at the rate of 30 min(-1). The performance of the met hod is examined for a wide range of parameters and is superior to that of other linear and nonlinear techniques. In the magnetospheric state representation the coupling is modeled as a small number of nonlinear equations under a time-dependent input.