On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual Values

The aa index can be decomposed into two separate components: the leading sporadic component due to solar activity as measured by sunspot number and the residual or recurrent component due to interplanetary disturbances, such as coronal holes. For the interval 1964–2006, a highly statistically important correlation (r=0.749) is found between annual averages of the aa index and the solar wind speed (especially between the residual component of aa and the solar wind speed, r=0.865). Because cyclic averages of aa (and the residual component) have trended upward during cycles 11–23, cyclic averages of solar wind speed are inferred to have also trended upward.