Effects of density stratification on Rossby waves in deep atmospheres

TL;DR

This study derives radial eigenfunctions for Rossby waves in deep stellar atmospheres, revealing two wave cavities and suggesting potential surface observability of interior modes.

Contribution

It introduces a new method using Lagrangian pressure fluctuation to compute cleaner radial eigenfunctions in a general stratification, applicable to the solar interior.

Findings

Identified two wave cavities in the solar interior: radiative zone and convection zone.

Radial vorticity eigenfunctions in the radiative interior are nearly constant in the convection zone.

The new approach avoids internal singularities present in previous models.

Abstract

Though Rossby waves have been observed on the Sun, their radial eigenfunctions remain a mystery. The 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. This project calculates the radial eigenfunctions for Rossby waves in a deep atmosphere for a general stratification. Here, we use the $\beta$-plane approximation to derive a vertical equation in terms of the Lagrangian pressure fluctuation $\delta P$, and 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 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.