Simulations of a cold front by cloud-resolving, limited-area, and large-scale models, and a model evaluation using in situ and satellite observations

The Global Energy and Water Cycle Experiment has identified the poor repres entation of clouds in atmospheric general circulation models as one of the major impediments for the use of these models in reliably predicting future climate change. One of the most commonly encountered types of cloud system in midlatitudes is that associated with cyclones. The purpose of this stud y is to investigate the representation of frontal cloud systems in a hierar chy of models in order to identify their relative weaknesses. The hierarchy of models was classified according to the horizontal resolution: cloud-res olving models (5-km resolution), limited-area models (20-km resolution), co arse-grid single-column models (300 km), and an atmospheric general circula tion model (>100 km). The models were evaluated using both in situ and sate llite data. The study shows. as expected. that the higher-resolution models give a more complete description of the front and capture many of the observed nonline ar features of the front. At the low resolution, the simulations are unable to capture the front accurately due to the lack of the nonlinear features seen in the high-resolution simulations. The model intercomparison identifi ed problems in applying single-column models to rapidly advecting baroclini c systems. Mesoscale circulations driven by subgrid-scale dynamical, thermo dynamical, and microphysical processes are identified as an important feedb ack mechanism Linking the frontal circulations and the cloud held. Finally it is shown that the same techniques used to validate climatological studie s with International Satellite Cloud Climatology Project data are also vali d for case studies. thereby providing a methodology to generalize the singl e case studies to climatological studies.