Effects of small‐scale dynamo and compressibility on the Λ effect

Abstract

The Λ effect describes a rotation‐induced nondiffusive contribution to the Reynolds stress. It is commonly held responsible for maintaining the observed differential rotation of the Sun and other late‐type stars. Here, the sensitivity of the Λ effect to small‐scale magnetic fields and compressibility is studied by means of forced turbulence simulations either with anisotropic forcing in fully periodic cubes or in density‐stratified domains with isotropic forcing. Effects of small‐scale magnetic fields are studied in cases where the magnetic fields are self‐consistently generated by a small‐scale dynamo. The results show that small‐scale magnetic fields lead to a quenching of the Λ effect which is milder than in cases where also a large‐scale field is present. The effect of compressibility on the Λ effect is negligible in the range of Mach numbers from 0.015 to 0.8. Density stratification induces a marked anisotropy in the turbulence and a vertical Λ effect if the forcing scale is roughly two times larger than the density scale height.