Solar Magnetic Field Signatures in Helioseismic Splitting Coefficients

TL;DR

This study uses helioseismic splitting coefficients to analyze the evolution of solar magnetic fields during cycle 23, revealing a combination of poloidal and toroidal fields with specific strengths and surface activity correlations.

Contribution

It introduces a method to infer large-scale magnetic field configurations in the solar interior from helioseismic data, highlighting the near-surface magnetic field structures during solar cycle 23.

Findings

Identified a poloidal dipole field with peak strength 124 G.

Detected two toroidal fields near the surface with strengths up to 1.4 kG.

Found magnetic field strengths correlate with surface activity and show hysteresis effects.

Abstract

Normal modes of oscillation of the Sun are useful probes of the solar interior. In this work, we use the even-order splitting coefficients to study the evolution of magnetic fields in the convection zone over solar cycle 23, assuming that the frequency splitting is only due to rotation and a large scale magnetic field. We find that the data are best fit by a combination of a poloidal field and a double-peaked near-surface toroidal field. The toroidal fields are centered at r=0.999R_solar and r=0.996R_solar and are confined to the near-surface layers. The poloidal field is a dipole field. The peak strength of the poloidal field is 124 +/- 17G. The toroidal field peaks at 380 +/- 30G and 1.4 +/- 0.2kG for the shallower and deeper fields respectively. The field strengths are highly correlated with surface activity. The toroidal field strength shows a hysteresis-like effect when compared to the global 10.7 cm radio flux. The poloidal field strength shows evidence of saturation at high activity.