Eigenvalues c = c_r + ic_i in the complex plane for kR = 10 and Re = 300, normalized by the reference eigenvalue |c₀|=(β − U″)/k². The R mode is clearly identifiable (the least damped mode), as are the three families of modes: the wall modes (A family), the center modes (P family), and the damped modes (S family). The modes with symmetric eigenfunctions are shown with full circles and those with antisymmetric eigenfunctions with open circles. All modes have c_r <  0 and c_i <  0, i.e., they are stable and propagate in the retrograde direction. The vertical line corresponds to the phase speed of the standard Rossby wave, c_r = c₀. The modes in each family are labeled with integers that increase with attenuation.