Seasonal Gyres in the Northern Gulf of California

Abstract

The circulation pattern in the northern Gulf of California, based on drifting buoys and hydrographic observations, can be explained using the results of a linear two-layer primitive equations model forced, at the annual frequency, by the Pacific Ocean, wind stress, and heat flux through the surface. The modeled surface circulation consists of a cyclonic gyre from June to October and an anticyclonic gyre from December to April, both located in the central region of the northern Gulf of California, which includes ?ngel de la Guarda Island. The maximum intensities of the gyres occur in August and February, respectively, with values of surface velocities of 65 cm s?1 (in agreement with the observations) and very low opposite velocities in the bottom layers. May and November are transition months in which both gyres can be observed. Finally, in June/July or December/January the growing gyre is still connected with the rest of the Gulf of California, through the narrows between Tiburón Island, San Esteban Island, and the Baja California coast, whereas from August through October and from February through April the respective gyre is isolated. The vertical structure of the model results indicates a mainly baroclinic signal both in the southern and central regions of the Gulf of California. In the northern gulf, however, the velocities in the annual signal are a combination of barotropic and baroclinic movements, with similar intensities, coupled by topography effects. Thus, only part of the dynamics is associated to great movements of the interface, which shows maximum values of 40 m.