Influence of the viscosity on the eigenvalues and eigenfunctions of the R, A₁, and P₁ modes. (a): real (solid curves) and imaginary (dashed curves) parts of the frequencies of the modes R, A₁, and P₁ for m = 2 as a function of the Ekman number in the case of the observed solar surface rotation profile. Panels b–g: real (top panels) and imaginary (bottom panels) parts of the stream functions for the same modes at three selected values for the Ekman number. See also the top panels of Fig. C.3 for a 2D representation of the stream functions for these modes.