Dissipation Efficiency in Turbulent Convective Zones in Low Mass Stars

TL;DR

This paper calculates effective viscosities in the convective zones of low-mass stars, extending previous models and providing new numerical prescriptions for different stellar periods and directions.

Contribution

It introduces revised effective viscosity calculations for stellar convective zones, improving upon previous models with detailed normalization and applicability to longer periods.

Findings

Effective viscosity scales linearly with period.

Magnitudes are at least three times larger than Zahn's prescription.

Results applicable for periods up to the convective turnover time.

Abstract

We extend the analysis of Penev et al. (2007) to calculate effective viscosities for the surface convective zones of three main sequence stars of 0.775Msun, 0.85Msun and the present day Sun. In addition we also pay careful attention to all normalization factors and assumptions in order to derive actual numerical prescriptions for the effective viscosity as a function of the period and direction of the external shear. Our results are applicable for periods that are too long to correspond to eddies that fall within the inertial subrange of Kolmogorov scaling, but no larger than the convective turnover time, when the assumptions of the calculation break down. We find linear scaling of effective viscosity with period and magnitudes at least three times larger than the Zahn (1966, 1989) prescription.