Projected climate change scenario over California by a regional ocean–atmosphere coupled model system
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This study examines a future climate change scenario over California in a 10-km coupled regional downscaling system of the Regional Spectral Model for the atmosphere and the Regional Ocean Modeling System for the ocean forced by the global Community Climate System Model version 3.0 (CCSM3). In summer, the coupled and uncoupled downscaled experiments capture the warming trend of surface air temperature, consistent with the driving CCSM3 forcing. However, the surface warming change along the California coast is weaker in the coupled downscaled experiment than it is in the uncoupled downscaling. Atmospheric cooling due to upwelling along the coast commonly appears in both the present and future climates, but the effect of upwelling is not fully compensated for by the projected large-scale warming in the coupled downscaling experiment. The projected change of extreme warm events is quite different between the coupled and uncoupled downscaling experiments, with the former projecting a more moderate change. The projected future change in precipitation is not significantly different between coupled and uncoupled downscaling. Both the coupled and uncoupled downscaling integrations predict increased onshore sea breeze change in summer daytime and reduced offshore land breeze change in summer nighttime along the coast from the Bay area to Point Conception. Compared to the simulation of present climate, the coupled and uncoupled downscaling experiments predict 17.5 % and 27.5 % fewer Catalina eddy hours in future climate respectively.
This work was supported by grants from National Oceanic and Atmospheric Administration (ECPC: NA17RJ1231, NA12OAR4310078, NA10OAR4310215, NA11OAR4310110), the California Energy Commission PIER Program, U.S. Geological Survey (06HQGR0125), and U.S. Department of Agriculture (027865). The views expressed herein are those of the authors and do not necessarily reflect the views of funding agencies. Supercomputing resources were provided by the Center for Observations, Modeling and Prediction at Scripps Institution of Oceanography and TACC via Extreme Science and Engineering Discovery Environment. The help of Kathy Fearon in refining our text is appreciated. Three anonymous reviewers helped to improve the manuscript.
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