Probability distributions of the average Alfvén speed, v_A, computed over the effective area of swirls identified between z = 600 km and z = 900 km. The total kernel density estimate is shown in black. The distributions are divided according to the average plasma-β conditions computed over the effective area of the swirls. The nonmagnetic category corresponds to plasma-β > 2.0, the mixed category corresponds to 0.5 < plasma-β ≤ 2.0, and the magnetic category corresponds to plasma-β ≤ 0.5. The red area and vertical dashed line correspond to the 5–95 percentile range and the median of the average sound speed computed over the effective area of the swirls, respectively.