Response of the magnetosphere to perturbation by storms and Alfvén wave trains

We investigate AE time series at one-minute sampling intervals under (a) geomagnetic storm Dst index below -100 nT, (b) weak geomagnetic activity Dst>-20nT, and high-intensity, long-duration continuous auroral activity (HILDCAA). The Takens estimator of correlation dimension and an ensemble of surrogate data sets were calculated for these conditions. No conclusive indication of deterministic behavior was found. The predictability was studied for all series and for surrogated sets. The case corresponding to HILDCAA was the most predictable and the one with the lowest correlation dimension. Thus the magnetosphere during an HILDCAA event may act as a stationary excited system.