Dispersion relations of the Rossby modes inside the RZ with ℓ = m (navy blue), ℓ = m + 1 (red), and ℓ = m + 2 (dark green) for azimuthal orders 1 ≤ m ≤ 16. The frequencies are measured in the Carrington frame. Plus symbols (n_RZ = 0) and open circles (n_RZ = 4) denote modes with different numbers of radial nodes, n_RZ, in the region 0.5 R_⊙ ≤ r ≤ 0.71 R_⊙. Solid grey curves represent the theoretical dispersion relations of the classical Rossby modes ${\omega }_{\ell ,m}^{\mathrm{R}}$ given by Eq. (14). The dashed black line denotes the maximum possible value of ${\omega }_{\ell ,m}^{\mathrm{R}}$.