Solar wind drivers of geomagnetic storms over more than four solar cycles

Using a classification of near-Earth solar wind flows into corotating high-speed streams, slow interstream solar wind, and transients originating with coronal mass ejections at the Sun, we determine the drivers of geomagnetic storms of various sizes from 1964 to 2011 based on the Kp index, encompassing more than four solar cycles. We also briefly discuss storm occurrence rates since the beginning of Kp in 1932.