Letter to the Editor

Simulations of entropy rain-driven convection

Institute for Solar Physics (KIS), Georges-Köhler-Allee 401a, 79110 Freiburg, Germany

^⋆ Corresponding author: pkapyla@leibniz-kis.de

Received: 1 April 2025
Accepted: 11 May 2025

Abstract

Context. The paradigm of convection in solar-like stars is questioned based on recent solar observations.

Aims. The primary aim is to study the effects of surface-driven entropy rain on convection zone structure and flows.

Methods. Simulations of compressible convection in Cartesian geometry with non-uniform surface cooling are used. The cooling profile includes localised cool patches that drive deeply penetrating plumes. Results are compared with cases with uniform cooling.

Results. Sufficiently strong surface driving leads to strong non-locality and a largely subadiabatic convectively mixed layer. In such cases the net convective energy transport is done almost solely by the downflows. The spatial scale of flows decreases with an increasing number of cooling patches for the vertical flows, whereas the maximum power for horizontal flows still occurs at largest scales.

Conclusions. To reach the plume-dominated regime with a predominantly subadiabatic bulk of the convection zone requires significantly more efficient entropy rain than what is realised in simulations with uniform cooling. It is plausible that this regime is realised in the Sun but that it occurs on scales smaller than those resolved in current simulations. Current results show that entropy rain can lead to a largely mildly subadiabatic convection zone, whereas its effects for the scale of convection are more subtle.