Characterization of solar-cycle induced frequency shift of medium- and high-degree acoustic modes

TL;DR

This paper investigates how solar activity influences the frequency shifts of medium- and high-degree acoustic modes, revealing a quadratic relation and a power-law scaling with mode inertia, enhancing understanding of solar oscillation behavior.

Contribution

It provides new insights into the dependence of solar acoustic mode frequency shifts on solar activity and mode inertia, including a quadratic relation and a frequency-dependent power law.

Findings

Frequency increases with solar activity, showing a quadratic relation.

Frequency shift scales with mode inertia following a power law.

The power law exponent decreases by 37% for frequencies above 2.5 mHz.

Abstract

Although it is well known that the solar acoustic mode frequency increases as the solar activity increases, the mechanism behind it is still unknown. Mode frequencies with 20 < l < 900 obtained by applying spherical harmonic decomposition to MDI full-disk observations were used. First, the dependence of solar acoustic mode frequency with solar activity was examined and evidence of a quadratic relation was found indicating a saturation effect at high solar activity. Then, the frequency dependence of frequency differences between the activity minimum and maximum was analyzed. The frequency shift scaled by the normalized mode inertia follows a simple power law where the exponent for the p modes decreases by 37% for modes with frequency larger than 2.5 mHz.