Fully Convective Magnetorotational Turbulence in Stratified Shearing Boxes

TL;DR

This study numerically investigates turbulence and dynamo action in stratified shearing boxes with zero magnetic flux, revealing the robustness of fully convective states under different boundary conditions and their impact on heat transport.

Contribution

It demonstrates the persistence of fully convective states in stratified shearing boxes with radiative boundary conditions, expanding understanding of turbulence and dynamo processes.

Findings

Fully convective states form regardless of boundary conditions.

Convective heat transport occurs via overturning motions.

Mean stratification remains non-adiabatic despite negligible diffusive transport.

Abstract

We present a numerical study of turbulence and dynamo action in stratified shearing boxes with zero magnetic flux. We assume that the fluid obeys the perfect gas law and has finite (constant) thermal diffusivity. We choose radiative boundary conditions at the vertical boundaries in which the heat flux is propor- tional to the fourth power of the temperature. We compare the results with the corresponding cases in which fixed temperature boundary conditions are applied. The most notable result is that the formation of a fully convective state in which the density is nearly constant as a function of height and the heat is transported to the upper and lower boundaries by overturning motions is robust and persists even in cases with radiative boundary conditions. Interestingly, in the convective regime, although the diffusive transport is negligible the mean stratification does not relax to an adiabatic state.