Observations of upwelling and relaxation events in the northern Monterey Bay during August 2000

Abstract

The interplay between the Point Año Nuevo upwelling center, an offshore anticyclonic mesoscale eddy, and the waters of the Monterey Bay was studied during a series of up- and downwelling favorable wind events during August 2000. The upwelling events were characterized by the appearance of cold, salty water at Point Año Nuevo at the north end of the bay that subsequently spread southward across the mouth of the bay as the winds continued. During the downwelling/relaxation events, the surface current and temperature response was dominated by the onshore translation of the offshore eddy and by local surface heating in the bay itself. The circulation within the bay was cyclonic during both wind regimes but slightly more barotropic under poleward forcing. The ICON model, a nested, data assimilating, sigma coordinate model, was used to simulate the upwelling and relaxation events and calculate the subsurface current and density fields. The model reproduced the dominant current and temperature patterns outside the bay, including the southward flowing upwelling filament, the movement of the offshore eddy, the poleward flow off Point Sur, and the circulation within the bay. The model salinity fields at the surface and 100 m levels show that during upwelling, the bay was filled with higher-salinity water stemming from the Point Año Nuevo upwelling center to the north. During downwelling, the source water for both the surface and 100 m levels was the colder, fresher California Current water offshore, which had advected southward well past Point Piños during the previous upwelling event. Copyright 2005 by the American Geophysical Union.