Climate signatures of the wind stress and wind stress curl over the U.S. West Coast

Long-term regional scale simulations of U.S. coastal offshore regions were conducted using the WRF model with inputs from the CCSM3 climate model. A horizontal resolution of 12 km was applied to the West Coast simulations for a period 1998-2007. The optimum physical parameterizations were selected after multi-annual sensitivity tests. The simulations during the upwelling period were able to reproduce observed characteristics of the sequences of the wind maxima in the lees of major capes and minima on the upwind sides as well as the positive wind stress curl in the offshore belt along the coast. This feature persisted throughout the ten-year period. The wind stress curl was computed for major upwelling areas in the less of Point Arena, Point Sur, Cape Mendocino and Cape Blanco and the results were analyzed with respect to the El Nino Southern Oscillation (ENSO) index. The comparison showed that the wind stress curl is inversely proportional to both indices. This implies that the larger wind stress and the positive wind stress curl generating coastal upwelling can be expected during El Nino periods and the opposite effect during La Nina conditions. The comparison with the PDO index shows similar behavior, but with somewhat smaller correlations. According to the results, the strongest climate signal was in the lees of Point Sur, Point Arena, and Point Conception.