Asymmetry in Solar Torsional Oscillation and the Sunspot Cycle

TL;DR

This study analyzes 16 years of helioseismic data to reveal hemispherical asymmetries in solar torsional oscillations, their relation to magnetic activity, and potential for predicting sunspot cycle asymmetries.

Contribution

It provides the first long-term analysis of hemispherical asymmetry in solar torsional oscillations and links these asymmetries to magnetic flux and sunspot activity.

Findings

Significant hemispherical asymmetry in torsional oscillation velocity.

Asymmetry in velocity precedes magnetic flux and sunspot number asymmetries.

Velocity asymmetry correlates with surface magnetic activity and sunspot cycle variations.

Abstract

Solar torsional oscillations are migrating bands of slower- and faster-than-average rotation, which are strongly related to the Sun's magnetic cycle. We perform a long-term study (16 yr) of hemispherical asymmetry in solar torsional oscillation velocity using helioseismic data for the first time. We study the north-south asymmetry in the velocity using the zonal flow velocities obtained by ring diagram analysis of the Global Oscillation Network Group (GONG) Doppler images. We find significant hemispherical asymmetry in the torsional oscillation velocity and explore its variation with respect to depth, time, and latitude. We also calculate the hemispherical asymmetry in the surface velocity measurements from the Mount Wilson Observatory and the zonal flow velocities obtained from the Helioseismic and Magnetic Imager ring diagram pipeline. These asymmetries are found to be consistent with the asymmetry obtained from GONG observations. We show that the asymmetry in near-surface torsional oscillation velocity is correlated with the asymmetry in magnetic flux and sunspot number at the solar surface, with the velocity asymmetry preceding the flux and sunspot number asymmetries. We speculate that the asymmetry in torsional oscillation velocity may help in predicting the hemispherical asymmetry in sunspot cycles.