DECAY OF CONVECTIVE TURBULENCE REVISITED

Results of a large-eddy simulation of a decaying convective mixed laye r over land are presented. The time evolution of the mixed layer is fo rced by the surface heat flux gradually decreasing with time. The resu lts obtained show that the decay of the turbulent kinetic energy is go verned by two scales, the external time scale controlling the surface heat flux changes, and the convective time scale. During the simulatio n, large eddies persist even when the heat flux at the surface becomes negative. A decoupled residual layer of active turbulence is develope d above the stable surface layer. The residual layer is marked by larg e-scale updrafts that are able to penetrate the capping inversion laye r and induce entrainment.