Statistical Downscaling and Forecast of Global Warming Reverse-Reaction Coastal Cooling in the California South Coast Air Basin
In this report, the evolution in time of the summer coastal cooling in the SoCAB is tested against global records and global circulation models (GCMs) in anticipation of forecasting future trends. Previous efforts in using GCMs to detect summer coastal cooling in California have reflected coastal-inland thermal gradients, however, failed to detect the magnitude of the decadal temperature decrease, attributed to lack of specificity of the local physical processes caused by local topography. For this study, a statistical downscaling approach is first used from the World Climate Research Programme's (WCRP's) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset under present climate conditions (1960-2010) and validated against present data. The statistical downscaling techniques are based on linear regression between temperature and large scale atmospheric forcing in order to obtain forecasted average surface temperatures at resolutions of 1/8 degrees from the 2 degree resolution of General Circulation Models (GCM). A Thin Plate Smoothing Spline interpolation technique is also used to improve the regression models. Results with the proposed approach show good agreement with present tendencies. For future conditions (2010-2050) it was found that summer coastal cooling has an increasing tendency consequence of the increased pressure gradient caused by the faster heating rate of inland regions in contrast to the slower heating rate of the sea surface temperatures. These future tendencies are modulated by the Pacific Decadal Oscillation, which controls the coastal upwelling.