Improving Rainfall Processes in Climate Models

Long-term ARM data used to evaluate precipitation simulations.

Image courtesy of Jared Tarbell, Flickr
By comparing computational simulations of rainfall with long-term measurements, researchers hope to improve how precipitation is represented in climate models.

The Science

Precipitation is one of the most poorly simulated physical processes in general circulation models (GCMs). Modeling precipitation is difficult because the variety of complex processes that influence it must be parameterized in large-scale models.

The Impact

Different model performances and associations with large-scale forcing and thermodynamic factors shed useful insights on cloud and convection parameterizations and will guide development of future models with improved precipitation representations.


The single-column model (SCM), which isolates a single grid column from a global model, is a useful and effective tool for studying parameterization schemes in GCMs. However, most SCM intercomparison studies with Atmospheric Radiation Measurement (ARM) data focus on special cases or week-to-month-long periods. To make a statistically meaningful comparison and evaluation of modeled precipitation, researchers have completed SCM simulations of seven GCMs participating in the  “FASTER” project led by Brookhaven National Laboratory and compared the models’ performance to 3 years of observations at the ARM Southern Great Plains site. Results show that, although most SCMs can reproduce observed precipitation reasonably well, significant differences and deficiencies exist. These include problems in frequency-intensity trade-off during cold seasons, too much rain during the day rather than at night, and differences in how various models partition rain between convective and stratiform clouds. Further analysis reveals distinct meteorological backgrounds for model precipitation underestimation and overestimation, offering clues to why the models are deficient.


Hua Song
Atmospheric Sciences Division, Brookhaven National Laboratory, 75 Rutherford Drive, Bldg. 815E, Upton, NY 11973-5000


This work is supported by the Earth System Modeling program within the Department of Energy’s Office of Biological and Environmental Research.


Song, H., et al. “Evaluation of precipitation simulated by seven SCMs against the ARM observation at the SGP site.” J. Climate, in press. [DOI: 10.1175/JCLI-D-12-00263.1].

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Program: BER , CESD

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