Swaying oscillations in Rayleigh-Bénard convection cast new light on solar convection

Horizontally periodic Boussinesq Rayleigh-Bénard convection (RBC) is a simple model system for studying the formation of large-scale structures in turbulent convective flows. We performed a suite of 2D numerical RBC simulations between no-slip boundaries at different Prandtl (Pr) and Rayleigh (Ra) numbers, such that their product was representative of the upper solar convection zone. When the fluid viscosity was sufficiently low (Pr ≲ 0.1) and turbulence was strong (Ra > 106), large structures began to couple in time and space. For Pr = 0.01, we observed long-lived swaying oscillations of the upflows and downflows that synchronized over multiple convection cells. This new regime of oscillatory convection might offer an interpretation of the wave-like properties of the dominant convection scale on the Sun (supergranulation).