Solar Meridional Flow in the Shallow Interior during the Rising Phase of Cycle 24

TL;DR

This study investigates the subsurface meridional and zonal flows during the rising phase of solar cycle 24, revealing hemispheric asymmetries, flow variations with magnetic activity, and an anti-correlation between flow speed and magnetic flux transport.

Contribution

It provides new insights into the behavior of solar interior flows and their relationship with magnetic activity during a solar cycle, using helioseismology data.

Findings

Hemispheric asymmetries in zonal flow patterns.

Meridional flow decreases with increased magnetic activity.

Anti-correlation between flow speed and poleward magnetic flux transport.

Abstract

Solar subsurface zonal and meridional-flow profiles during the rising phase of solar cycle 24 are studied using time-distance helioseismology technique. The faster zonal bands in the torsional-oscillation pattern show strong hemispheric asymmetries and temporal variations in both width and speed. The faster band in the northern hemisphere is located closer to the equator than the band in the southern hemisphere, and migrates past the equator when the magnetic activity in the southern hemisphere is reaching maximum. The meridional-flow speed decreases substantially with the increase of magnetic activity, and the flow profile shows two zonal structures in each hemisphere. The residual meridional flow, after subtracting a mean meridional-flow profile, converges toward the activity belts and shows faster and slower bands like the torsional-oscillation pattern. More interestingly, the meridional-flow speed above latitude 30 degree shows an anti-correlation with the poleward-transporting magnetic flux, slower when the following-polarity flux is transported and faster when the leading-polarity flux is transported. It is expected that this phenomenon slows the process of magnetic cancellation and polarity reversal in the high-latitude areas.