Swaying oscillations in Rayleigh-B\'enard convection cast new light on solar convection

Abstract

Horizontally-periodic Boussinesq Rayleigh-B\'enard Convection (RBC) is a simple model system to study the formation of large-scale structures in turbulent convective flows. We performed a suite of 2D numerical simulations of RBC between no-slip boundaries at different Prandtl (Pr) and Rayleigh (Ra) numbers, such that their product is representative of the Sun's upper convection zone. When the fluid viscosity is sufficiently low (Pr $\lesssim 0.1$) and turbulence is strong (Ra $> 10^6$) we find that large structures begin to couple in time and space. For Pr = 0.01 we observe long-lived swaying oscillations of the upflows and downflows, which synchronize over multiple convection cells. This new regime of oscillatory convection may offer an interpretation for the wave-like properties of the dominant scale of convection on the Sun (supergranulation).