On the Statistics of the Seasonal Geomagnetic Variations.

We analyze the data sets of daily average Dst (1957-2005) and Ap (1932-2005) indices. Differential and integral statistical distribution functions of geomagnetic perturbations versus their strength constructed. First moments of the distributions calculated. Asymptotic behavior of the distributions at extremely low and high magnetic activity as well as around mean and most probable states obtained for the whole data sets and for the selected periods of time (spring and autumn, summer and winter) around equinoxes and solstices. We confirm and extend the results of some previous studies. Absolute and relative amplitudes of seasonal geomagnetic variations interpreted as a consequence of the non-linear magnetospheric response to the solar and heliospheric drivers.