GEOMAG DRIVERS. “The coherent magnetic field structure, the strongly varying field and plasma density in the sheath region preceding the ICME proper, the fast solar wind speed, as well as the interplanetary shock itself are all effective drivers of geomagnetic activity.” (ICME= Interplanetary coronal mass ejection).
https://link.springer.com/article/10.12942/lrsp-2007-1