Ring current decay rates of magnetic storms:: A statistical study from 1957 to 1998 -: art. no. 1059

[1] We perform a statistical study of the decay times for the recovery phase of the 300 most intense magnetic storms that occurred from 1 January 1957 to 31 December 1998. The Dst index in the decaying stage has been fitted by an exponential function, and a very good correlation has been obtained for most of the storms. Statistically representative values for the decay time (tau) are obtained by averaging the most reliable tau values, which resulted from applying a least squares method to the Dst index time series during every recovery phase. The mean value of tau turned out to be similar to14 +/- 4 hours. We have also found that for very intense storms (Dst(min) < -250 nT) the values of tau tend to decrease as the intensity of the storm increases.