Bivariate distribution of the local average Alfvén speed, ⟨v_A⟩_swirl, and the average estimated rotational velocity of the swirl, at the bottom of the chromosphere (z = 700 km). The averages are computed over the swirl area. The average plasma-β over the swirl area is color coded. A power-law fit of the type y = ax^b is shown in dashed black. The fitted parameters are a = 0.16,  b = 1.13. Density contours of the scattered points are shown in gray.