Relative Contributions of Coronal Mass Ejections and High-speed Streams to the Long-term Variation of Annual Geomagnetic Activity: Solar Cycle Variation and Latitudinal Differences

Coronal mass ejections (CMEs) and high-speed solar wind streams (HSSs) are the most important large-scale solar wind structures driving geomagnetic activity. It is well known that CMEs cause the strongest geomagnetic storms, while HSSs drive mainly moderate or small storms. Here we study the spatial-temporal distribution of geomagnetic activity at annual resolution using local geomagnetic indices from a wide range of latitudes in 1966-2014. We show that the overall contribution of HSSs to geomagnetic activity exceeds that of CMEs at all latitudes. Only in a few sunspot maximum years CMEs have a comparable contribution to HSSs. While the relative contribution of HSSs maximizes at high latitudes, the relative contribution of CMEs maximizes at subauroral and low latitudes. We show that this is related to different latitudinal distribution of CME and HSS-driven substorms. We also show that the contributions of CMEs and HSSs to annual geomagnetic activity are highly correlated with the intensity of the interplanetary magnetic field and the solar wind speed, respectively. Thus, a very large fraction of the long-term variability in annual geomagnetic activity is described only by the variation of IMF strength and solar wind speed.