Unexpected solar-cycle variation of acoustic mode power in Sun-as-a-star observations

TL;DR

This study analyzes 45 years of helioseismic data revealing that acoustic mode power varies with the solar cycle, showing complex relationships with magnetic activity that differ from mode frequency responses.

Contribution

It provides a robust analysis of solar-cycle variations in helioseismic mode power using long-term data, highlighting unexpected similarities between different solar cycles.

Findings

Mode power varies with the solar cycle in the five-minute band.

Cycle 24's weaker magnetic activity did not significantly reduce mode power compared to Cycle 23.

Mode frequencies correlate strongly with magnetic activity, unlike mode power.

Abstract

We examine the solar-cycle variation of the power in the low-degree helioseismic modes by looking at binned power spectra from 45 years of observations with the Birmingham Solar Oscillations Network, which provides a more robust estimate of the mode power than that obtained by peak fitting. The solar-cycle variation of acoustic mode power in the five-minute band is clearly seen. Unusually, even though Cycle 24 was substantially weaker in terms of surface magnetic activity than Cycle 23, the reduction in mode power at solar maximum is very similar for the two cycles, suggesting that the relationship between mode power and magnetic activity is more complex than has previously been thought. This is in contrast to the mode frequencies, which show a strong correlation with activity with only subtle differences between in the response across different solar cycles.