Comparison of LES model produced and in-situ measured stratocumulus cloud microphysics

Abstract:

Large Eddy Simulation (LES) models are known to be a valuable tool that can be used to study microphysical, dynamical and radiative properties and their complex interactions in stratocumulus clouds since they can generate stratocumulus clouds realistically. These model generated properties were often compared with observations usually focusing on macroscopic features such as cloud depth and LWP. In this study we try to examine how good LES models are in re-producing cloud microphysical characteristics of stratocumulus clouds. After all if microphysics is not right, macroscopic, dynamic and radiative characteristics represented by the model cannot be fully trusted. The observation data are obtained from the G-1 aircraft measurements of marine stratocumulus clouds over the southeast Pacific near the coast of Chile during the Variability of the American Monsoon Systems Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). Two LES models are used to simulate these clouds: one is CIMMS (Cooperative Institute for Mesoscale Meteorological Studies) LES and the other is WRF (Weather Research and Forecasting Model) LES. Both models are run in 3-D setting and employ bin microphysics to be appropriate for detailed cloud microphysics calculation. Comparison between observation and LES models could reveal intrinsic problems of the LES models in representing entrainment and mixing processes. The difference between the two LES models may reveal the intrinsic differences between the two models in representing large eddies and microphysical processes. Some preliminary results indicate that the CIMMS LES model tends to produce cloud microphysical relationships that are expected to occur when homogeneous mixing is dominant. More detail will be presented at the conference.