Solar wind speed V_p (Figure 9)

The P₂ (4-8 mHz) and P₅ (32-64 mHz) events occurred more frequently at high solar wind speeds. This is especially clear for the P₅ events. The occurrence rates for the P₃ (8-16 mHz) and P₄ (16-32 mHz) events maximize when V_p = 400-450 km/s and V_p = 500-550 km/s, respectively, but neither case has a high normalized occurrence rate when the solar wind speed is higher than 550 km/s.

Figure 9. Normalized occurrence rates for $P_2, \ldots , P_5$ events at different solar wind speeds.