Frequency of the torsional wave (normalised by the Alfvén wave frequency) versus the longitudinal wave number for typical parameters of a solar plasma structure. The solid lines are obtained numerically from Eq. (19) while the dashed lines are plotted from the analytic expression represented by Eq. (20). For the blue lines we have 𝒦 = 0.4, ℛ = 0.1, while for the red lines we have 𝒦 = 0.1, ℛ = 0.4.