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

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.

arXiv comment9 pages, 6 figures. Accepted by MNRAS 24 May 2017

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Cited by in corpus (10)

• Solar cycle prediction
• Solar structure and evolution
• Changes in the solar rotation over two solar cycles
• On Midrange Periodicities in Solar Radio Flux and Sunspot Areas
• Changes in the sensitivity of solar p-mode frequency shifts to activity over three solar cycles
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• Helioseismology and solar neutrinos
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