Changes in solar oscillation frequencies during the current activity maximum: analysis and interpretation

TL;DR

This paper analyzes how solar oscillation frequencies change with the solar activity cycle, revealing a seismic map that correlates frequency shifts with magnetic field evolution across different latitudes.

Contribution

It provides the first comprehensive seismic map of solar activity changes across all latitudes during cycle 23, linking frequency variations to magnetic field evolution.

Findings

Frequency shifts closely follow the butterfly diagram at low latitudes.

Significant activity detected in polar regions during solar minimum.

Magnetic field changes of about 100 G are responsible for frequency variations.

Abstract

We describe systematic changes in the centroid frequencies and the splitting coefficients as found using data from MDI on board SOHO, covering cycle 23. The data allow us to construct a seismic map of the evolving solar activity -- covering all latitudes. At lower latitudes, the temporal evolution closely tracks that of {\it butterfly diagram}. The additional information from higher latitudes in the map is of a significant activity in the polar region, peaking at activity minimum in 1996. The most plausible source of solar oscillation frequency changes over the solar cycle is the evolution of the radial component of the small-scale magnetic field. The amplitude of the required mean field changes is about 100 G at the photosphere, and increasing going inward.