The influence of winds and topography on the sea surface temperature patterns over the northern California slope

Abstract

As part of the Coastal Ocean Dynamics Experiment (CODE), 56 infrared images from the NOAA 6 satellite were analyzed and compared with in situ data to investigate the relationship between SST (sea surface temperature) patterns and winds, topography, and adjusted sea level (ASL) off northern California. After extensive processing to eliminate clouds and to obtain better temperature accuracy, the decimated images were decomposed into mean SST and empirical orthogonal functions (EOF) by using a method developed for a large and gappy set of data. The SST EOF's were compared with EOF's of wind stress and ASL. The first SST mode (in order of variance) described a seasonal warming trend that was somewhat modified by large‐scale wind events. Comparison of the time‐varying amplitudes of SST with those of wind stress and ASL showed that the second and third SST functions described locally driven coastal upwelling that is modified by shelf topography. This analysis suggested that an irregular coastline generates irregular upwelling patterns in response to a spatially uniform wind stress and that the upwelling response propagates northward in conjunction with a northward propagating wind system. Further, the apparent cold‐water sources of the long cold plumes seen in satellite images were shown to be regions of enhanced coastal upwelling associated with capes. These regions extend from the coast across the continental shelf, suggesting that the plumes are anchored to coastal topography.