Wave frequency in the inertial frame as expected to be seen by observations vs. ε. The frequency was normalised by the angular frequency of a star, Ω. Black, blue, and red curves correspond to the modes with l = 0, l = 2, and l = 4, respectively. The left panels display the Rossby modes with m = 1 (solid lines, upper panel) and m = 2 (dashed lines, lower panel). The upper (lower) right panel shows inertia-Gravity modes (Rossby-gravity modes). Grey dashed lines denote the value of ε calculated for the solar parameters and the equivalent depth of h = 0.0064 H₀.