Numerical Simulation of Cloud–Clear Air Interfacial Mixing

Abstract

Abstract This paper discusses results from a series of direct numerical simulations of the microscale cloud–clear air mixing, set forth in the idealized scenario of decaying moist turbulence. In the moist case, kinetic energy of microscale motions comes not only from the classical downscale energy cascade, but it can also be generated internally due to the evaporation of cloud droplets. Three sets of numerical simulations are performed for three intensities of initial large-scale eddies. In each set, a control dry simulation is performed, as well as two moist simulations applying either bulk or detailed representation of cloud microphysics. Model results suggest that, as far as the evolutions of enstrophy and turbulent kinetic energy are concerned, the most significant impact of moist processes occurs at the low intensity of initial large-scale eddies (the input turbulent kinetic energy of 2 × 10−4 m2 s−2 resulting in the maximum eddy dissipation rate of 5 × 10−4 m2 s−3). In such a case, mixing and homoge...