# The Sun in transition? Persistence of near-surface structural changes through Cycle 24

## TL;DR

This study analyzes helioseismic frequency shifts over three solar cycles, revealing changes in their correlation with solar activity and suggesting a possible fundamental shift in the solar dynamo process.

## Contribution

It provides a long-term analysis of helioseismic data, highlighting changes in the frequency response to solar activity across multiple cycles and proposing a potential dynamo transition.

## Key findings

- Medium- and high-frequency shifts correlate well with activity indices.
- Reduced correlation of low-frequency shifts with activity in cycles 23 and 24.
- Increased sensitivity to activity in medium and high frequencies in recent cycles.

## Abstract

We examine the frequency shifts in low-degree helioseismic modes from the Birmingham Solar-Oscillations Network (BiSON) covering the period from 1985 - 2016, and compare them with a number of global activity proxies well as a latitudinally-resolved magnetic index. As well as looking at frequency shifts in different frequency bands, we look at a parametrization of the shift as a cubic function of frequency. While the shifts in the medium- and highfrequency bands are very well correlated with all of the activity indices (with the best correlation being with the 10.7 cm radio flux), we confirm earlier findings that there appears to have been a change in the frequency response to activity during solar cycle 23, and the low frequency shifts are less correlated with activity in the last two cycles than they were in Cycle 22. At the same time, the more recent cycles show a slight increase in their sensitivity to activity levels at medium and higher frequencies, perhaps because a greater proportion of activity is composed of weaker or more ephemeral regions. This lends weight to the speculation that a fundamental change in the nature of the solar dynamo may be in progress.