Polar-wave deformation-radius identifiability

For a polar gamma-plane Rossby wave, the drift fixes ${\alpha }^2=K^2+L_d^{-2}$. It does not separately fix radial wavenumber $K$ and Rossby deformation radius $L_d$. Scaling an eigenfunction changes its amplitude without changing either wavenumber, so a meander amplitude cannot supply the missing radial wavelength. A radial boundary condition or a separately justified envelope approximation is needed to determine $L_d$.