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Radiative Heating Profiles in the Tropics – An Evaluation of Model Output Using ARM Observations

McFarlane, Sally Pacific Northwest National Laboratory
Mather, James Pacific Northwest National Laboratory
Ackerman, Thomas DOE/Pacific Northwest National Laboratory

The variability of water vapor and clouds in the atmosphere, and their associated radiative heating, is an important driver of atmospheric circulation. While we have good knowledge of radiative fluxes at the top of the atmosphere and at specific surface sites, observations of atmospheric profiles of radiative heating in the tropics, particularly in cloudy conditions, have been largely unavailable. Current estimates of cloudy sky radiative heating in the tropics are typically based on model simulations, residuals from total heat and moisture budgets, or satellite observations. The long time series of observations taken at the ARM sites on Nauru and Manus provides a more direct method of calculating all sky heating rate profiles with high vertical and temporal resolution. We have calculated radiative heating rate profiles for several months at each of these sites using observed and retrieved inputs of water vapor, condensed water, phase, particle size, and mass. The accuracy of the profiles can be assessed by comparing the calculated TOA and surface fluxes with observations. This study presents an initial evaluation of the ability of several large scale models to reproduce radiative heating rate profiles in the tropics. We compare the calculated heating rate dataset to model output from the European Center for Medium-Range Weather Forecasting (ECMWF) analysis, the NCAR Community Atmosphere Model (CAM 3.0), and the Multi-Scale Modeling Framework (MMF). These three models, all run using observed SST for this comparison, provide an interesting range of resolution from the 4 km cloud resolving model in the MMF to the 280 km grid-scale of the CAM. In general, the model results fail to capture some of the structure of the observed heating because their vertical resolution is too coarse to fully resolve the shallow boundary layer clouds and they tend to have too little cirrus and stratiform cloud, which is often placed too high in the troposphere.

This poster will be displayed at the ARM Science Team Meeting.