Monday

Space weather impacts on grounds infrastructure are expected to increase primarily with geomagnetic storm intensity, but also storm duration. It is therefore important to understand the degree to which these storm characteristics are correlated. We use the recent recalibration of the long-running aa index, aa_H, to analyse the relationship between geomagnetic storm intensity and storm duration over the past 150 years, further adding to our understanding of the climatology of geomagnetic activity. Using a threshold approach to storm definition, we find that more intense storms have longer durations, as expected, and that the distribution of durations for a given intensity is approximately log-normal. On this basis, we provide a method for probabilistically predicting storm duration given its peak intensity and test this against the aa_H data set. By considering the average profile of storms we show that activity becomes less recurrent on the 27-day timescale with increasing intensity.