Intraseasonal Variation of Winter Precipitation over the Western United States Simulated by 14 IPCC AR4 Coupled GCMs

This study evaluates the intraseasonal variation of winter precipitation over the western United States in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century...

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Bibliographic Details
Published in:	Journal of climate 2010-06, Vol.23 (11), p.3094-3119
Main Authors:	Lin, Jia-Lin, Shinoda, Toshiaki, Qian, Taotao, Han, Weiqing, Roundy, Paul, Zheng, Yangxing
Format:	Article
Language:	eng
Subjects:	20th century Atmosphere Atmospherics Barotropic mode Climate change Climate models Climatology. Bioclimatology. Climate change Convection Datasets Earth, ocean, space Exact sciences and technology External geophysics General circulation models Horizontal cells Humidity Intergovernmental Panel on Climate Change International environmental cooperation Intraseasonal variations Madden-Julian oscillation Mean precipitation Meteorology Meteors Modeling Modelling Precipitation Propagation Rain Seasonal variations Simulation Simulations Statistical discrepancies Studies Teleconnections Variability Vertical profiles Water in the atmosphere (humidity, clouds, evaporation, precipitation) Winter Winter precipitation
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Summary:	This study evaluates the intraseasonal variation of winter precipitation over the western United States in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. The focus is on the two dominant intraseasonal modes for the western U.S. precipitation: the 40-day mode and the 22-day mode. The results show that the models tend to overestimate the northern winter (November–April) seasonal mean precipitation over the western United States and Canada. The models also tend to produce overly strong intraseasonal variability in western U.S. wintertime precipitation, in spite of the overly weak tropical intraseasonal variability in most of the models. All models capture both the 40-day mode and the 22-day mode, usually with overly large variances. For the 40-day mode, models tend to reproduce its deep barotropic vertical structure and three-cell horizontal structure, but only 5 of the 14 models capture its northward propagation, and only 2 models simulate its teleconnection with the Madden–Julian oscillation in the tropical Pacific. For the 22-day mode, 8 of the 14 models reproduce its coherent northward propagation, and 9 models capture its teleconnection with precipitation in the tropical Pacific.
ISSN:	0894-8755 1520-0442