Large-scale Vortices in Rapidly Rotating Rayleigh–Bénard Convection at Small Prandtl number

Abstract

Abstract One prominent feature in the atmospheres of Jupiter and Saturn is the appearance of large-scale vortices (LSVs). However, the mechanism that sustains these LSVs remains unclear. One possible mechanism is that these LSVs are driven by rotating convection. Here, we present numerical simulation results on a rapidly rotating Rayleigh–Bénard convection at a small Prandtl number Pr = 0.1 (close to the turbulent Prandtl numbers of Jupiter and Saturn). We identified four flow regimes in our simulation: multiple small vortices, a coexisting large-scale cyclone and anticyclone, large-scale cyclone, and turbulence. The formation of LSVs requires that two conditions be satisfied: the vertical Reynolds number is large ( Re z ≥ 400 ), and the Rossby number is small (Ro ≤ 0.4). A large-scale cyclone first appears when Ro decreases to be smaller than 0.4. When Ro further decreases to be smaller than 0.1, a coexisting large-scale cyclone and anticyclone emerges. We have studied the heat transfer in rapidly rotating convection. The result reveals that the heat transfer is more efficient in the anticyclonic region than in the cyclonic region. Besides, we find that the 2D effect increases and the 3D effect decreases in transporting convective flux as the rotation rate increases. We find that aspect ratio has an effect on the critical Rossby number in the emergence of LSVs. Our results provide helpful insights into understanding the dynamics of LSVs in gas giants.