On the cause of geomagnetic activity at Hale sector boundary

The solar wind velocity and density have been studied around the interplanetary magnetic field sector boundaries (+ to ? and ? to +) during 1965–1974, separating the data into autumnal and vernal periods. It is noticed that the solar wind velocity shows a sharp increase around the Hale type of sector boundary in both northern and southern heliosphere indicating a more favourable condition for the high speed stream after Hale type of sector boundary crossing than non-Hale boundary.