Relating Integral Latent Heat Release to Integral Mass Flux in Cumulus Convective Clouds.

Parameters of latent heat release were analyzed using LES model data. The system of trade wind cumulus clouds observed during the RICO field project was simulated over a domain size of a mesoscale model grid. The initialization of simulations were described in detail in the LES model intercomparison study by van Zanten et al 2011. Over 2000 clouds were analyzed focusing on relationship between parameters of latent heat release (phase transition rates) and dynamical/microphysical cloud characteristics.

Thephase transition rates, which in warm tropical clouds are represented by processes of condensation/evaporation, were analyzed by stratifying the clouds by their size/stage of maturity. The analyzed parameters included, among others, integral mass and buoyancy fluxes, cloud and rain water parameters, supersaturation. In addition to phase transition processes, we also analyzed the formation of precipitation and its dependence on cloud dynamical parameters. Of particular interest was the ratio of precipitation to condensation rate, which can be considered as an indicator of cloud “precipitation efficiency” (PE=PR/CR). We found that a critical vertical cloud depth separates clouds where PE is predominantly  < 1, from clouds where precipitation efficiency is mostly larger than one

The investigation of the relationships between phase transion rates and  cloud thermodynamical parameters revealed a remarkably strong correlation  between integral latent heat released in a cloud and its integral mass flux. The anticipated dependence on buoyancy flux was significanly weaker.

The identified latent heat-mass flux dependency and, based upon it, derived simple functional formulation can be important for the development of parameterization of subgrid latent heat release in meso- and large-scale forecast models.