Temporal evolution and parameter correlations of the switchback occurrence rate. Left: 27-day sliding averages of the switchback occurrence rate (O_R, blue) and sunspot number (SSN, gray) in panel (a), along with two Alfvénicity indices–$\overline{E_{\mathit{rr}}}$ (red; panel (b)) and $\overline{{\sigma }_c}$ (green; panel (c)). Panel (d): Bivariate distribution of $\overline{E_{\mathit{rr}}}$ vs. SSN, with point size representing relative frequency and color indicating mean O_R in each parameter bin. Panel (e): Same as (d), but with the y-axis replaced by the normalized SSN (denoted SSN^*), obtained by dividing the SSN by its maximum value within each solar cycle.