Constrained water cloud generator

The fast generation of large cloudy volumes with imposed cloud cover fractions and ambient vertical profiles is very important for the realistic simulation of atmospheric scenes. The model proposed here is the second step of a two-step model composed on the one hand of a volume generator based on a Fourier filtering method and on the other hand of a physical generator filling the volume with physical parameters. a description of the general generation scheme, this paper focuses on the simulation of vertical profiles of water content (liquid, vapour) coupled with other state parameters (temperature, pressure, vertical velocity) via thermodynamic and hydrodynamic equations by local forcing of ambient conditions. The method for solving these equations is explained and applied to practical cases. by assuming that the actual temperature at the cloud base is equal to the dew temperature and by imposing a moist pseudo-adiabatic temperature gradient between the cloud top and bottom, the temperature profile in the cloud is found. When conditional instability occurs, the initial temperature profile between the ground and the cloud base is iteratively shifted to lower values until absolute stability is reached. Then the liquid water content is calculated by integrating the equation of water conservation, and the water vapour content by assuming that the cloud is everywhere saturated. Eventually, the vertical velocity is estimated by integration of the momentum equation. ethod gives results in good agreement with published measurements, analytical and numerical models. Eventually, further developments of the column model, including the effects of phase transitions, turbulence, horizontal motions and mixing with the surrounding medium, are proposed in the concluding section.