Normalized phase speed Eq. (5) V_ph/V_ph(0) vs. the dimensionless depth z/h for the fast kink modes for AR 11726 (left panel) and AR 11327 (right panel). In either of these cases, we consider four options for the surface value of the plasma mass density: ρ₀ = ρ_e (blue curves), ρ₀ = ρ_e/ 2 (red curves), ρ₀ = ρ_e/ 4 (green curves) and ρ₀ = ρ_e/ 6 (black curves), respectively. In addition, it should be noted that we here show curves for four different depth of the wave turning point viz. h = 10000km (solid line curves), h = 20000km (dashed line curves), h = 40000km (dotted-dashed line curves) and h = 200000km (dotted line curves).