Turbulent thermal convection in a rotating stratified fluid

Abstract

Turbulent convection induced by heating the bottom boundary of a horizontally homogeneous, linearly (temperature) stratified, rotating fluid layer is studied using a series of laboratory experiments. It is shown that the growth of the convective mixed layer is dynamically affected by background rotation (or Coriolis forces) when the parameter R = (h²Ω³/q₀)^2/3 exceeds a critical value of R_c ≈ 275. Here h is the depth of the convective layer, Ω is the rate of rotation, and q₀ is the buoyancy flux at the bottom boundary. At larger R, the buoyancy gradient in the mixed layer appears to scale as (db/dz)_ml = CΩ², where C ≈ 0.02. Conversely, when R < R_c, the buoyancy gradient is independent of Ω and approaches that of the non-rotating case. The entrainment velocity, u_e, for R > R_c was found to be dependent on Ω according to E = [Ri(1 + CΩ²/N²)]⁻¹, where E is the entrainment coefficient based on the convective velocity w∗ = (q₀h)^1/3, E = u_e/w∗, Ri is the Richardson number Ri = N²h²/w²∗, and N is the buoyancy frequency of the overlying stratified layer. The results indicate that entrainment in this case is dominated by non-penetrative convection, although the convective plumes can penetrate the interface in the form of lenticular protrusions.