Effects of Density Stratification on Rossby Waves in Deep Atmospheres

Abstract Though Rossby waves have been observed on the Sun, their radial eigenfunctions remain a mystery. Prior theoretical work either considers quasi-2D systems, which do not apply to the solar interior, or only considers fully radiative or fully convective atmospheres. Here, we derive a radial wave equation that is valid for Rossby waves in a deep atmosphere with a general gravitational stratification. We adopt the β -plane approximation and express our equations in terms of the Lagrangian pressure fluctuation δP . We then calculate radial eigenfunctions for Rossby waves in a standard solar model, Model S. We find that working in the Lagrangian pressure fluctuation results in cleaner wave equations that lack the internal singularities that have been encountered in prior work. The resulting radial wave equation makes it abundantly clear that there are two wave cavities in the solar interior, one in the radiative interior and another in the convection zone. Surprisingly, our calculated radial vorticity eigenfunctions for the radiative interior modes are nearly constant throughout the convection zone, raising the possibility that they may be observable at the solar surface.