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

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.

10 pages, 5 figures, revised version published in A&A (high-resolution vector-graphics figures available in the journal version)

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Cited by in corpus (5)

• Imaging the Sun's near-surface flows using mode-coupling analysis
• Implicit large eddy simulations of global solar convection: effects of numerical resolution in non-rotating and rotating cases
• Characterising solar surface convection using Doppler measurements
• Texture of average solar photospheric flows and the donut-like pattern
• Investigating toroidal flows in the Sun using normal-mode coupling