Lambda effect from forced turbulence simulations^*

¹ Observatory, PO Box 14, 00014 University of Helsinki, Finland e-mail: petri.kapyla@helsinki.fi
² NORDITA, AlbaNova University Center, Roslagstullsbacken 23, 10691 Stockholm, Sweden

Received: 19 November 2007
Accepted: 22 May 2008

Abstract

Aims. We determine the components of the Λ-effect tensor that quantifies the contributions to the turbulent momentum transport even for uniform rotation.

Methods. Three-dimensional numerical simulations are used to study turbulent transport in triply periodic cubes under the influence of rotation and anisotropic forcing. Comparison is made with analytical results obtained via the so-called minimal tau-approximation.

Results. In the case where the turbulence intensity in the vertical direction dominates, the vertical stress is always negative. This situation is expected to occur in stellar convection zones. The horizontal component of the stress is weaker and exhibits a maximum at latitude  – regardless of how rapid the rotation is. The minimal tau-approximation captures many of the qualitative features of the numerical results, provided the relaxation time tau is close to the turnover time, i.e. the Strouhal number is of order unity.