A SIMULATION OF THE STORM-TIME RING CURRENT

The formation of a closed ring current from a partial ring current is examined quantitatively by a particle trajectory tracing method. That is, we simulated the storm-time ring current by a model with monochromatic energy and pitch angle distribution using a dipole magnetic field with a time-varying electric field. It is found that the combination of the particle energy and the temporal variation of the cross-tail electric field can generate various patterns of the ring current development. It is also found that the recovery of the ring current is explained by the superposition of the "flow out" effect and the loss process of trapped particles by charge exchange. We estimated the geomagnetic Dst, index from the particle motions and obtained results similar to the actual Dst recovery with two different time constants. © 1990.