Validating Model Clouds and Their Optical Properties Using Geostationary Satellite Imagery

A real-time validation scheme for diagnosing radiatively active clouds has been in operation for a number of years at the Australian Bureau of Meteorology. It compares IR channel imagery from four geostationary satellites and equivalent forward calculations using fields from the bureau's global and regional NWP models. The scheme also attempts to glean some information about cloud amounts from the satellite data for direct comparison with the model but is hampered by the reliance on a single spectral channel. A new radiance code derived from the Edwards and Slingo radiation scheme and several cloud optical property schemes has recently been implemented into the system. The forward calculations were performed using both the operational radiative transfer code and this new code, and the results were compared with satellite measurements. The effects of different cloud optical property schemes, cloud particle scattering, and cloud phase state were investigated. The results have shown a dramatic improvement in the comparison due to changes in the model physical parameterizations. The major achievement obtained in this study is the implementation of a new ice water content diagnostic scheme developed on the basis of lidar-radar data collected at the Southern Great Plains, the cloud and radiation test bed site of the Atmospheric Radiation Measurement (ARM) Program in Oklahoma. Using this scheme in the cold cloud temperature region (T < -50 degree C) in conjunction with the new forward radiance code, the modeled brightness temperature using fields from the global NWP model is significantly improved.