Helioseismic Imaging of Fast Convective Flows Throughout the Near-Surface Shear Layer

TL;DR

This study uses advanced helioseismic techniques to map and analyze the strength, scale, and rotational influence of convective flows throughout the Sun's near-surface shear layer, revealing depth-dependent flow speeds and rotational effects.

Contribution

It introduces a new implementation of ring-diagram helioseismology with high-resolution measurements and efficient 3D inversion, providing detailed insights into convective motions and rotational influence in the near-surface shear layer.

Findings

Peak horizontal flow speed of 427 m/s at the photosphere

Flow speed decreases to 124 m/s at 20-30 Mm depth

Rotational influence transitions from low near surface to significant at the base

Abstract

Using a new implementation of ring-diagram helioseismology, we ascertain the strength and spatial scale of convective flows throughout the near-surface shear layer. Our ring-diagram technique employs highly overlapped analysis regions and an efficient method of 3D inversion to measure convective motions with a resolution that ranges from $3 \ \mathrm{Mm}$ at the surface to $80 \ \mathrm{Mm}$ at the base of the layer. We find the rms horizontal flow speed to peak at $427 \ \mathrm{m \ s^{-1}}$ at the photosphere and fall to a minimum of $124 \ \mathrm{m \ s^{-1}}$ between $20 \ \mathrm{Mm}$ and $30 \ \mathrm{Mm}$. From the velocity amplitude and the dominant horizontal scales seen at each depth, we infer the level of rotational influence on convection to be low near the surface, but transition to a significant level at the base of the near-surface shear layer with a Rossby number varying between 2.2 to as low as 0.1.