Rotation suppresses giant-scale solar convection

Abstract

The observational absence of giant convection cells near the Sun’s outer surface is a long-standing conundrum for solar modelers. We herein propose an explanation. Rotation strongly influences the internal dynamics, leading to suppressed convective velocities, enhanced thermal-transport efficiency, and (most significantly) relatively smaller dominant length scales. We specifically predict a characteristic convection length scale of roughly 30-Mm throughout much of the convection zone, implying weak flow amplitudes at 100- to 200-Mm giant cells scales, representative of the total envelope depth. Our reasoning is such that Coriolis forces primarily balance pressure gradients (geostrophy). Background vortex stretching balances baroclinic torques. Both together balance nonlinear advection. Turbulent fluxes convey the excess part of the solar luminosity that radiative diffusion cannot. We show that these four relations determine estimates for the dominant length scales and dynamical amplitudes strictly in terms of known physical quantities. We predict that the dynamical Rossby number for convection is less than unity below the near-surface shear layer, indicating rotational constraint.

Exploring Ocean Circulation on Icy Moons Heated From Below

“…According to Figure 9d, we find that L ≈ 20 H Ro* 1/2 = 20 l ρ for the simulations where Ro* < 0.01. This scaling law compares favorably with that derived by equating the vortex stretching and inertial terms in the vorticity budget (Featherstone & Hindman, 2016) and is also close to that presented in Aurnou et al (2020) and Vasil et al (2021) where, in the rapidly rotating limit, they suggest L ∼ H Ro* 2/5 (see Appendix A for a further discussion).…”

“…(2020) and Vasil et al. (2021) where, in the rapidly rotating limit, they suggest L ∼ H Ro * 2/5 (see Appendix for a further discussion).…”

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

“…Here we present a simple discussion of small-scale magnetic fields in the presence of convection and speculate on how those fields could affect flicker measurements. Numerous, more advanced approaches exist in the literature (e.g., Gough & Tayler 1966;Knölker & Schüssler 1988;Cattaneo et al 2003;MacDonald & Mullan 2014, and references therein); however, our discussion is based on first-principles arguments of convective force balances, which have very successfully described convection in the presence of both strong and weak global rotation (reviewed and applied to the Sun respectively in Aurnou et al 2020;Vasil et al 2020).…”

Experimental pub crawl from Rayleigh–Bénard to magnetostrophic convection

“…The canonical source of dynamo-generating fluid motions in planets and stars is buoyancy-driven convection (e.g. Cheng et al 2015;Vasil, Julien & Featherstone 2021). Thus, in order to elucidate geophysical and astrophysical dynamo generation mechanisms, it is necessary to illuminate their underlying convective flows, and how they are affected by rotational and magnetic forces.…”