Models of Dst geomagnetic activity and of its coupling to solar wind parameters

Nonlinear filters have provided high-accuracy predictions of geomagnetic activity indices from solar wind key parameters. Here we extend the nonlinear prediction methods to derive closed-form analytical models for the solar wind-geomagnetic coupling. For each phase of either storm or magnetopause compression as identified by D-st, we calculate nonlinear, piecewise-constant models of the relation between the ring current index D-st and the solar wind electric field components. The time scales of storm main phase and recovery depend on storm phase, and the presence of solar wind VBs and pressure. Then, going beyond piecewise constant models, we use state space methods to reveal the fine structure of the D-st dynamics in detail. (C) 1998 Elsevier Science Ltd. All rights reserved.