Changes in the near-surface shear layer of the Sun

TL;DR

This study analyzes helioseismic data over two solar cycles to investigate how the near-surface shear layer of the Sun varies with the solar cycle, revealing latitude-dependent and depth-dependent changes.

Contribution

It provides the first detailed analysis of the solar-cycle dependence of the near-surface shear layer's depth and radial gradient using helioseismic data.

Findings

Radial gradient of rotation rate varies with the solar cycle.

Changes are more pronounced at active latitudes.

The shear layer is deeper at lower latitudes.

Abstract

We use helioseismic data obtained over two solar cycles to determine whether there are changes in the near-surface shear layer (NSSL). We examine this by determining the radial gradient of the solar rotation rate. The radial gradient itself shows a solar-cycle dependence, and the changes are more pronounced in the active latitudes than at adjoining higher latitudes; results at the highest latitudes (greater than about70 degrees) are unreliable. The pattern changes with depth, even within the NSSL. We find that the near-surface shear layer is deeper at lower latitudes than at high latitudes and that the extent of the layer also shows a small solar-cycle related change.