Power spectra of latitudinal velocity v_θ near the equator (averaged over ±15 deg). Panels a and b: m − ω diagram near the base (r = 0.75 R_⊙) and near the surface (r = 0.95 R_⊙), respectively. The power is normalized at each m. The spectra are computed in a frame rotating at Ω₀/2π = 431.3 nHz. Overplotted in red line in panel a is the dispersion relation of the equatorial Rossby mode with no radial node (n = 0) obtained from the linear calculation. The blue line represents the advection frequency of the equatorial differential rotation, m[Ω(r,π/2)−Ω₀], at each height. Panels c and d: power spectra at fixed azimuthal order m = 1 and m = 16, respectively.