06/06/2012

Weather Prediction Model Evaluation Using ARM Data

Summary

The long-term measurement records from the Atmospheric Radiation Measurement (ARM) site on the Southern Great Plains (SGP) show evidence of a surface irradiance bias in the global Numerical Weather Prediction model from the European Centre for Medium-Range Weather Forecasts (ECMWF). This has been a long-standing problem in the model, and previous studies have suggested that low clouds may contribute. To guide improvements to the model’s cloud and radiation parameterizations, the origin of the bias was explored for different cloud regimes to highlight the particular cloud processes that are contributing to the error. Comparisons between observed and modeled cloud fraction profiles over six years at the SGP site identified overcast low cloud conditions during the spring and fall seasons as a major contributor to the model bias. These findings will provide guidance for a targeted improvement of cloud parameterizations.

References

Ahlgrimm, M., and R. Forbes. 2012. “The Impact of Low Clouds on Surface Shortwave Radiation in the ECMWF Model,” Monthly Weather Review, DOI: 10.1175/MWR-D-11-00316.1.