92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012
Detection of Global Warming Reverse-Reaction Coastal Cooling Along the Entire California Coast
Hall E (New Orleans Convention Center )
Pedro sequera, City College of New York, New York, NY; and J. Gonzalez, R. Bornstein, and A. T. Ghebreegziabher

Previous studies conducted by Lebassi et al. (2009) analyzed summer surface June, July and August (JJA) mean monthly maximum air temperature trends between 1950-2005 for two California air basins, i.e., San Francisco Bay Area (SFBA) and South Coast Air Basin (SoCAB), by use of daily data from 273 National Weather Service (NWS) Coop sites. The spatial distribution of the observed JJA max temperatures showed a complex pattern, in which cooling trends were found at low elevation coastal areas open to marine air penetration and warming trends at inland and high elevation coastal areas. As a consequence of the thus increased gradient of the concurrent sea breeze potential for the same period, the authors suggested that this increased sea breeze activity was responsible for the observed coastal cooling. Other recent reports have detected coastal cooling along the South America Pacific coast. This work extends such coastal cooling analyses for all of the California coast. Maximum monthly summer Tmax trends for the 1970-2010 period were calculated for 241 locations in the entire state of California by use of daily max temperatures from NWS Coop sites. Maximum monthly values were selected instead of the average monthly values to avoid biases produced by selection of summer months. Statistical analyses through boxplots and hypothesis tests were used to classify locations according to their elevation and distance from the coast to determine the spatial extent of the coastal cooling effect. In addition, cross-section profiles at 10, 50 and 100 km from the coast were obtained to evaluate the extent of the intensity of the signal. Results show that almost all locations that present a cooling trend are located below 100 m above sea-level and at distances less than 70 km. from the coast. It was also found that maximum coastal cooling occurs at different air basins as those reported by Lebassi et al. (2009), i.e., in the Northern part of the State, about 200 km from the Northern boundary at Humbold County and also inthe San Diego area, withcoastal cooling levels of -0.666 and -1.3C/decade, respectively, reinforcing the hypothesis of sea-breeze impacts on climate change process.

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