Low Clouds Contribute to Weather Prediction Model Bias
Long-term measurement records improve the representation of clouds in climate and weather forecast models.
The Science
This study investigated and addressed biases and compensating errors in the surface radiation (radiation hitting the surface of the Earth), which are directly linked to cloud amount and properties, using data from the Southern Great Plains Atmospheric Radiation Measurement (ARM) Climate Research Facility.
The Impact
These findings will provide guidance for a targeted improvement of cloud parameterizations in climate and weather forecast models.
Summary
The long-term measurement records from the Atmospheric Radiation Measurement 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). Surface temperature, cloud cover and associated radiative processes need to be accurately represented. This has been a long-standing problem in the model and previous studies have suggested that low clouds may contribute. In order to guide improvements to the model's cloud and radiation parameterizations, the origin of the bias was explored for different cloud regimes in order 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 are identified as a major contributor to the model bias.
Contact
Dr. Maike Ahlgrimm
European Centre for Medium-Range Weather Forecasts
Great Britain
maike.ahlgrimm@ecmwf.int
Funding
Basic Research: DOE Office of Science, Office of Biological and Environmental Research
Publications
Ahlgrimm, Maike, Richard Forbes, 2012: The Impact of Low Clouds on Surface Shortwave Radiation in the ECMWF Model. Mon. Wea. Rev., 140, 3783–3794. DOI: http://dx.doi.org/10.1175/MWR-D-11-00316.1
Highlight Categories
Performer: Industry , SC User Facilities , BER User Facilities , ARM
