Hale sector boundary and geomagnetic activity

The variation of the geomagnetic activity index, Ap, at the IMF sector boundaries (+ to - and - to +) has been studied for three solar cycles, separating the data into vernal and autumnal equinoxes. It has been found that at the Hale boundary, geomagnetic activity index, Ap, shows a sharp increase compared to that around the non-Hale boundary. (author)