(a) Relation between the transmissivity of Alfvén waves (α_co/ph = L_A,co/L_Aout,ph) and the reflection rate of the photosphere (L_Ain,ph/L_Aout,ph). (b) Relation between α_co/ph and the normalized Alfvén wave travel time from the photosphere to the corona (τ_A,co, defined in Equation (77)) with respect to the acoustic cutoff frequency ν_ac.