The Response of Rotating Stellar Convection to Latitudinally-Varying Heat Flux

TL;DR

This study uses 3D simulations to explore how latitudinal heat flux variations influence rotating stellar convection, revealing impacts on thermal wind balance and differential rotation, with implications for understanding the Sun's near-surface shear layer.

Contribution

It demonstrates how imposed latitudinal heat flux variations affect thermal wind balance and differential rotation in rotating convection, providing insights into solar near-surface dynamics.

Findings

Differential rotation weakens with increased flux variation.

High Rossby number flows efficiently mix heat laterally.

Thermal wind balance breaks down at high Rossby numbers.

Abstract

We investigate how rotating convection responds to the imposition of a latitudinally-varying heat flux at the base of the convective layer. This study is motivated by the solar near-surface shear layer, whose flows are thought to transition from a buoyancy-dominated regime near the photosphere to a rotation-dominated regime at depth. Here, we conduct a suite of spherical 3-D, nonlinear simulations of rotating convection that operate in either the buoyancy-dominated (high-Rossby-number, high-Ro) or rotation-dominated (low-Rossby-number, low-Ro) regime. At the base of each model convection zone, we impose a heat flux whose latitudinal variation is opposite to the variation that the system would ordinarily develop. In both the low- and high-Ro regimes, a strong thermal wind balance is sustained in the absence of forcing. With a larger flux variation, this balance becomes stronger at high latitudes and weaker at low latitudes. The resulting differential rotation weakens in response and, at sufficiently high forcing, its latitudinal variation reverses for both low- and high-Ro systems. At fixed forcing, there exists a Rossby number above which the convective flows efficiently mix heat laterally, and the imposed flux variation does not imprint to the surface. At sufficiently high-Ro, thermal wind balance is no longer satisfied. We discuss these results within the context of the Sun's near-surface region, which possesses a weakened differential rotation when compared to the deep convection, along with little-to-no variation of photospheric emissivity in latitude.