Verification of LES warm rain microphysics and observational uncertainty

Traditional methods of model verification compare the first and, in some cases, the second PDF moments of predicted and observed cloud parameters. A more robust approach is to compare full PDFs of model and observational variables and study their dependence on environmental conditions.

We have analyzed PDFs of cloud liquid water and drop concentration during two research flights (RF01 and RF02) conducted during the DYCOMS-II field project. The study compares PDFs in non-precipitating clouds (RF01) with PDF in precipitating clouds. PDF width is dependent on the intensity of turbulence in precipitating clouds but rather insensitive to it in non-precipitating conditions. The latter reflects the fact that non-precipitating stratocumulus are more homogeneous. PDFs demonstrate strong scale dependence which needs to be taken into consideration when comparing LES model with observations. Accounting for this scale dependence is also important in representing model subgrid variability in calculations of unbiased microphysical process rates. The results of the study will lead to the development of more robust techniques of model and parameterization verification.