The existence of the Lambda effect in the solar convection zone indicated by SDO observations

TL;DR

This paper demonstrates the presence of the Lambda effect in the solar convection zone using SDO observations, showing it explains the observed angular momentum transport and differential rotation.

Contribution

It provides evidence for the Lambda effect in the solar convection zone and discusses its implications for solar differential rotation theories.

Findings

Horizontal Reynolds stress is negative at the surface in the northern hemisphere.

The Lambda effect causes positive horizontal Reynolds stress in the bulk of the convection zone.

The Lambda effect's angular momentum transport is proportional to the cube of the rotation rate.

Abstract

The empirical finding with data from the Solar Dynamics Observatory (SDO) of positive (negative) horizontal Reynolds stress at the northern (southern) hemisphere for solar giant cells (Hathaway et al. 2013) is discussed for its consequences for the theory of the solar/stellar differential rotation. Solving the nonlinear Reynolds equation for the angular velocity under neglect of the meridional circulation we show that the horizontal Reynolds stress of the northern hemisphere is always negative at the surface but it is positive in the bulk of the solar convection zone by the action of the Lambda effect. The Lambda effect, which describes the angular momentum transport of rigidly rotating anisotropic turbulence and which avoids a rigid-body rotation of the convection zones, is in horizontal direction of cubic power in the rotation rate $\Omega$ and it is always equatorwards directed. Theories without Lambda effect which may also provide the observed solar rotation law only by the action of a meridional circulation lead to a horizontal Reynolds stress with the opposite sign as observed.