A dearth of detailed cloud observations has encouraged large- scale modelers to utilize methods which employ cloud resolving models (CRMs) to evaluate the utility of cloud parameterizations. Albeit somewhat useful as a tool, the CRM generally leaves unanswered the essential question concerning the parameterization's validity. Herein we propose to examine one particular cloud parameterization developed by Xu and Randall (XR, 1996). Unlike cloud parameterizations involving probability distribution functions (PDFs), which require knowledge of the higher order moments of the subgrid variables, the XR technique depends only upon the large scale relative humidity and cloud and ice water mixing ratios.
We apply data obtained from the FIRE (First ISCCP Regional Experiment's) Atlantic Stratocumulus Transition Experiment. The liquid water path (LWP) measured from a microwave radiometer and the RH field obtained from sounding data are used as inputs to the XR stratus cloud parameterization and then compared with cloud fraction profiles determined from cloud radar measurements. Estimates of the parameterization's three free parameters are derived from these observations and then compared with the values obtained from the CRM simulations conducted by XR.
The 13th Symposium on Boundary Layers and Turbulence