Global-scale equatorial Rossby waves as an essential component of solar internal dynamics

TL;DR

This paper reports the first unambiguous detection of Rossby waves in the Sun's shallow subsurface layers, revealing their significant role in solar internal dynamics and energy distribution at large scales.

Contribution

It provides the first clear observational evidence of Rossby waves in the Sun, characterizing their properties and emphasizing their importance in solar convection and energy dynamics.

Findings

Detection of retrograde Rossby waves with months-long lifetimes

Rossby waves have vorticity comparable to convection at similar scales

Transition from turbulence-like to wave-like behavior around the Rhines scale

Abstract

The Sun's complex dynamics is controlled by buoyancy and rotation in the convection zone and by magnetic forces in the atmosphere and corona. While small-scale solar convection is well understood, the dynamics of large-scale flows in the solar convection zone is not explained by theory or simulations. Waves of vorticity due to the Coriolis force, known as Rossby waves, are expected to remove energy out of convection at the largest scales. Here we unambiguously detect and characterize retrograde-propagating vorticity waves in the shallow subsurface layers of the Sun at angular wavenumbers below fifteen, with the dispersion relation of textbook sectoral Rossby waves. The waves have lifetimes of several months, well-defined mode frequencies below 200 nHz in a co-rotating frame, 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 find a transition from turbulence-like to wave-like dynamics around the Rhines scale of angular wavenumber of twenty; this might provide an explanation for the puzzling deficit of kinetic energy at the largest spatial scales.