Multiscale Organization of Turbulent Convection in Global-Sun Simulations

Solar convection is at the core of fundamental phenomena such as differential rotation and meridional circulation and, ultimately, the solar dynamo. The governing mechanisms, amplitude, and dominant scales of convection in the solar interior remain under debate. Furthermore, the large Reynolds and Rayleigh numbers involved make it implausible to resolve all relevant scales using direct numerical simulation. In this work, we study solar convection through global, non-rotating, and non-magnetic implicit large-eddy simulations (ILES), using the 3D global hydrodynamic code EULAG. Our simulations exhibit a pattern of multiscale convection, clearly visible on the domain surface (~0.96 R), generated by a solar-like density and entropy stratification. Scale-splitting is evident at various depths throughout the model, with the upper boundary of convective cells penetrating surface layers, resembling solar-like convection. A continuous and coherent multiscale structure of convective cells is observed throughout the convective interior. The power peak of convective scales continuously shrinks with height to a maximum spherical harmonic degree of l = 40-50 on the model surface, compatible with reports of giant cell observations. Simulations are performed from low to high resolution to explore whether integral properties of convection, such as the RMS velocity, temperature profiles, and turbulent spectra, become independent of the mesh size. Results are compared with current observations of surface and sub-surface solar convection.