The Sun's complex dynamics is controlled by buoyancy and rotation in the convection zone. Large-scale flows are dominated by vortical motions and appear to be weaker than expected in the solar interior. One possibility is that waves of vorticity due to the Coriolis force, known as Rossby waves or r modes, remove energy from convection at the largest scales. However, the presence of these waves in the Sun is still debated. Here, we unambiguously discover and characterize retrograde-propagating vorticity waves in the shallow subsurface layers of the Sun at azimuthal wavenumbers below 15, with the dispersion relation of textbook sectoral Rossby waves. The waves have lifetimes of several months, well-defined mode frequencies below twice the solar rotational frequency, and eigenfunctions of vorticity that peak at the equator. Rossby waves have nearly as much vorticity as the convection at the same scales, thus they are an essential component of solar dynamics. We observe a transition from turbulence-like to wave-like dynamics around the Rhines scale of angular wavenumber of approximately 20. This transition might provide an explanation for the puzzling deficit of kinetic energy at the largest spatial scales.
ASJC Scopus subject areas
- Astronomy and Astrophysics