Effects of small‐scale wind on coastal upwelling with application to Point Conception

Abstract

A three‐dimensional, limited‐area, ocean general circulation model is used to study the response of the coastal ocean to small‐scale wind forcing. The model considers an idealized forcing of a semi‐infinite, upwelling‐favorable wind with a large positive wind curl at one end. Such a wind pattern is commonly found in the vicinity of capes and points where the synoptic‐scale wind is disturbed by coastal mountain ranges. The model study includes both process and hindcast studies. The process study considers the upwelling spinup and relaxation, driven by a positive wind curl. It also examines the model sensitivity to wind patterns and an external pressure force. The model results show that a strong poleward alongshore pressure gradient is set up by a positive wind curl. This pressure force drives an inshore poleward current into the upwelling region during active wind forcing, and it causes a surge of warm water into the upwelling zone during wind relaxation. The hindcast study is applied to the 1983 Organization of Persistent Upwelling Structures (OPUS) observations near Point Conception off central California. The simulation uses an idealized geometry but with observed winds. During OPUS, a sudden reversal of the surface equatorward currents occurred in the midst of a steady upwelling‐favorable wind. This unexpected coastal flow feature was faithfully reproduced in the model simulation.