Supergranulation and multiscale flows in the solar photosphere: Global observations vs. a theory of anisotropic turbulent convection

TL;DR

This paper combines global observations and a new anisotropic turbulence theory to better understand multiscale flows in the solar photosphere, especially supergranulation, revealing their anisotropic, buoyant, and self-similar nature.

Contribution

It introduces an anisotropic extension of the Bolgiano-Obukhov turbulence theory tailored for solar photospheric flows, linking observations with theoretical modeling.

Findings

Photospheric flows between supergranulation and granulation are vertically correlated over 2.5-4 Mm.

Flows operate in a strongly anisotropic, nonlinear, buoyant regime.

The theory offers a framework for future validation with high-resolution data.

Abstract

The Sun provides us with the only spatially well-resolved astrophysical example of turbulent thermal convection. While various aspects of solar photospheric turbulence, such as granulation (one-Megameter horizontal scale), are well understood, the questions of the physical origin and dynamical organization of larger-scale flows, such as the 30-Megameters supergranulation and flows deep in the solar convection zone, remain largely open in spite of their importance for solar dynamics and magnetism. Here, we present a new critical global observational characterization of multiscale photospheric flows and subsequently formulate an anisotropic extension of the Bolgiano-Obukhov theory of hydrodynamic stratified turbulence that may explain several of their distinctive dynamical properties. Our combined analysis suggests that photospheric flows in the horizontal range of scales between supergranulation and granulation have a typical vertical correlation scale of 2.5 to 4 Megameters and operate in a strongly anisotropic, self-similar, nonlinear, buoyant dynamical regime. While the theory remains speculative at this stage, it lends itself to quantitative comparisons with future high-resolution acoustic tomography of subsurface layers and advanced numerical models. Such a validation exercise may also lead to new insights into the asymptotic dynamical regimes in which other, unresolved turbulent anisotropic astrophysical fluid systems supporting waves or instabilities operate.