Cloud Occurrence Profiles in the TWP from High Resolution Models and Data

Abstract:

A simple, but important, measure of the ability of models to simulate cloud properties is whether the vertical structure of cloud occurrence in the model is consistent with that from data. Observed cloud occurrence profiles in the tropical western Pacific typically exhibit three peaks, one near the top of the boundary layer, one near the freezing level, and a broad peak in the upper troposphere. There is considerable variation in the overall probability of occurrence and strength of these peaks. Here, we investigate the ability of a new generation of high-resolution models to simulate these profiles. Our study uses GSRMs from the DYnamics of the Atmospheric general circulation On Non-hydrostatic Domains (DYAMOND) project. Nine models were run globally for 40 days starting from initial conditions on August 1, 2016. We use two data sources, the ARM site in Manus Island, Papua New Guinea, and the CERES SYN product, which relies on MODIS data for its cloud properties. The ARM profiles are obtained from a combination of millimeter radar and micropulse lidar data.

Our study consists of a determination of local variability in cloud occurrence profiles. We make use of the extended ARM data series to construct profiles for each August in the data series and for seasonal profiles for July, August and September (JAS). The ARM data are available at high frequency at a single location but the monthly average profiles are influenced by local weather variation. The CERES data are sampled over a broader spatial region but at lower spatial and temporal resolution. These two data sets provide us with an accurate assessment of cloud occurrence and a measure of internal variability. We compare the profiles from the models. The models are run at a resolution of a few kilometers and we evaluate profiles in a 10x10 lat-long area centered on the Manus ARM site. We consider profiles over the entire area and over a 1x1 cell located over the Manus site. This allows us to capture some sense of the spatial variability within each model and the model to model variability. Our results suggest that the models simulate the rough structure of cloud occurrence but that there are large differences in the relative strengths of the peaks among the models and the overall probability of occurrence. This presentation will provide a detailed assessment of these strength and weaknesses.