Fraction of swirls obeying Eq. (11), f_Alfévnic, as a function of height z. The green profile refers to all identified swirls, while the blue curve takes into account only those swirls that form coherent structures connecting the surface layers (z = 0 km) to the low chromosphere (z = 700 km). Shaded areas represent statistical standard deviations. The average optical surface τ₅₀₀ = 1 (z = 0 km) is marked by a dotted line, while the heights of the surface layers of the convection zone, photosphere, and low chromosphere used in the analysis are indicated by dashed blue lines.