Observation and Modeling of the Solar-Cycle Variation of the Meridional Flow

TL;DR

This study observes and models the solar-cycle variation of meridional flows at the solar surface and at 60 Mm depth, revealing opposite signs in their variations and comparing observations with a flux-transport dynamo model.

Contribution

It provides independent measurements of flow variations at different depths and tests their consistency with a theoretical flux-transport dynamo model.

Findings

Opposite signs in meridional flow variations at surface and 60 Mm depth.

In-phase variation of zonal flows at different depths.

Qualitative agreement between observations and the flux-transport dynamo model.

Abstract

We present independent observations of the solar-cycle variation of flows near the solar surface and at a depth of about 60 Mm, in the latitude range $\pm45^\circ$. We show that the time-varying components of the meridional flow at these two depths have opposite sign, while the time-varying components of the zonal flow are in phase. This is in agreement with previous results. We then investigate whether the observations are consistent with a theoretical model of solar-cycle dependent meridional circulation based on a flux-transport dynamo combined with a geostrophic flow caused by increased radiative loss in the active region belt (the only existing quantitative model). We find that the model and the data are in qualitative agreement, although the amplitude of the solar-cycle variation of the meridional flow at 60 Mm is underestimated by the model.