Asymmetry in seasonal variations of geomagnetic activity

Seasonal variations in geomagnetic activity were studied for the period of 1990-2007 using Dst and AE indices. Over 150 events characterised by the increase in geomagnetic activity of varying strength (from -90nT up to -1800 nT) were statistically analysed. Although Russell -McPherron effect plays major role in the equinoctial asymmetry in the geomagnetic activity, other effects may also take place. During this study we found a statistically significant October-November peak in geomagnetic activity for Northern Hemisphere, which is sufficiently larger than March- April peak. Several hypotheses for the cause of such effect are discussed.