Meridional flow profile measurements with SOHO/MDI

TL;DR

This paper introduces a new helioseismic method to measure the Sun's meridional flow at greater depths using SOHO/MDI data, revealing complex flow patterns that suggest multiple circulation cells.

Contribution

A novel helioseismic approach enabling deeper meridional flow measurements and evidence for multiple circulation cells in the solar convection zone.

Findings

Meridional flow is poleward in the upper convection zone.

Flow turns equatorward at about 40 Mm depth.

Possible existence of two circulation cells per hemisphere.

Abstract

We present meridional flow measurements of the Sun using a novel helioseismic approach for analyzing SOHO/MDI data in order to push the current limits in radial depth. Analyzing three consecutive months of data during solar minimum, we find that the meridional flow is as expected poleward in the upper convection zone, turns equatorward at a depth of around 40 Mm (~0.95 Rsol), and possibly changes direction again in the lower convection zone. This may indicate two meridional circulation cells in each hemisphere, one beneath the other.