A high-resolution ocean-atmosphere coupled downscaling of the present climate over California
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A fully coupled regional ocean-atmosphere model system that consists of the regional spectral model and the regional ocean modeling system for atmosphere and ocean components, respectively, is applied to downscale the present climate (1985–1994) over California from a global simulation of the Community Climate System Model 3.0 (CCSM3). The horizontal resolution of the regional coupled modeling system is 10 km, while that of the CCSM3 is at a spectral truncation of T85 (approximately 1.4°). The effects of the coupling along the California coast in the boreal summer and winter are highlighted. Evaluation of the sea surface temperature (SST) and 2-m air temperature climatology shows that alleviation of the warm bias along the California coast in the global model output is clear in the regional coupled model run. The 10-m wind is also improved by reducing the northwesterly winds along the coast. The higher resolution coupling effect on the temperature and specific humidity is the largest near the surface, while the significant impact on the wind magnitude appears at a height of approximately 850-hPa heights. The frequency of the Catalina Eddy and its duration are increased by more than 60 % in the coupled downscaling, which is attributed to enhanced offshore sea-breeze. Our study indicates that coupling is vital to regional climate downscaling of mesoscale phenomena over coastal areas.
KeywordsRegional climate Coupled model Ocean-atmosphere interaction CCSM3 RSM ROMS
Funding was provided by NOAA (ECPC: NA17RJ1231), the NSF (OCE-0960770), the California Energy Commission PIER Program, the Korea Meteorological Administration Research and Development Program under Grant CATER 2012-3084, and by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (2012-0000158). The views expressed herein are those of the authors and do not necessarily reflect the views of the NOAA. Supercomputing resources were provided by COMPAS at SIO and TACC via XSEDE. Two anonymous reviewers helped to improve the manuscript.
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