Structural Tilting and Depth-Dependent Behavior of Equatorial Rossby Waves

TL;DR

This study analyzes the depth-dependent structure and evolution of solar equatorial Rossby waves using helioseismology data, revealing stable retrograde tilts and their relation to solar interior dynamics over a solar cycle.

Contribution

It provides the first detailed investigation of the inclination and phase behavior of Rossby waves at multiple depths in the solar interior, using extensive helioseismology data.

Findings

Deeper depths lead in phase over shallower ones.

Rossby waves exhibit a stable retrograde tilt relative to solar rotation.

Cross power correlates positively with the solar cycle.

Abstract

Over the past decade, solar equatorial Rossby waves have been unambiguously identified and are considered potential diagnostics of solar interior dynamics. We investigate their inclined structure and temporal evolution in the solar interior across multiple depths using approximately 14.5 yr of ring-diagram (RD) and time-distance (TD) helioseismology data from SDO/HMI. Normalized phase differences and cross power are computed from filtered spherical harmonic coefficients of radial vorticity to probe the structural tilt and power of Rossby waves. We find a systematic and robust depth-dependent phase behavior that shows no clear significant correlation with the solar cycle, while the depth-dependent cross power exhibits a positive correlation with the solar cycle for both datasets. Our results show that deeper depths lead in phase over shallower ones, with increasing negative phases with depth. We infer that Rossby waves exhibit a retrograde tilt relative to the Sun's rotation that is stable throughout the solar cycle. Analogous small tilts have been noted in planetary atmospheres and in magnetohydrodynamic simulations of the Sun, indicating that this behavior is not uncommon in rotating, stratified bodies and has implications for angular momentum and energy transport in the solar interior.