Panels a–c: normalised chromospheric profiles reported in Fig. 12 of Fontenla et al. (1988; AR 2340, blue solid line) and observed on April 17, 2009 (red dashed line; Tian et al. 2009b), overlapped with a normalised Gaussian coronal absorption profile (black dotted line) computed by setting the coronal H I temperature to 1.5 × 10⁶ K, considering θ = 0°. Panels a–c: correspond to outflow velocities equal to v_w = 0 km s⁻¹, v_w = 150 km s⁻¹, and v_w = 300 km s⁻¹, respectively. In the case of the exciting narrowest profile, we also display the grey shaded area that is proportional to the product of the coronal absorption profile (Φ) and the chromospheric pumping profile (Ψ). Panel d: Doppler factor as a function of v_w calculated considering each chromospheric profile (AR 2340: blue solid line; polar CH: red dashed line). Triangles, squares and asterisks indicate the Doppler dimming values corresponding to H I outflow velocities equal to v_w = 0 km s⁻¹, v_w = 150 km s⁻¹, and v_w = 300 km s⁻¹, respectively.