Left panel: imaginary part of k as function of wave period (horizontal axis) and height (vertical axis) obtained after solving dispersion relation for two-fluid equations (Eq. (36)) for S magnetic field profile. Solution #3 from Fig. 13 is used. The period varies between 1 s and 20 s (the minimum and maximum values used in the simulations). The solid, black line represents the contour of k_I = 0. Right panel: imaginary part of k as function of background magnetic field at base of atmosphere (horizontal axis) and height (vertical axis). The wave period is fixed to 5 s.