How wall modes affect the onset and character of rapidly rotating Rayleigh-Bénard convection

Rotation and buoyancy drive many natural phenomena including atmospheric, oceanic, and inner Earth flows as well as convective processes in planetary atmospheres, in the dynamics of the sun, and in other astrophysical systems. An important experimental, computational, and theoretical system that incorporates many of the features of these more complex systems is rotating Rayleigh-Bénard convection. In rapidly rotating Rayleigh-Bénard convection, wall modes that precess in the rotating frame form the foundation for the onset of bulk convection especially in convection cells of small diameter-to-height ratio Γ. In doing so they reveal fascinating features of both instabilities [1]. Here, we consider direct numerical simulations of a fluid with Prandtl number Pr = 0.9 for Ekman number Ek = 10^-6 over a range of Rayleigh number 3 x 10⁷ ≤ Ra ≤ 5 x 10⁹. The convection cell geometry is cylindrical with aspect ratio Γ = 1/2. We describe detailed investigations of the complex interplay between wall modes and bulk flows including a subcritical bifurcation to lateral jet instability, contributions to heat transport from both instabilities, the disparate radial localization of temperature and velocity fields, and the evolving nonlinear character of wall modes that survive the onset and development of bulk instability leading to a robust boundary zonal flow (BZF) [2,3].