Short term variations of the anticyclonic circulation in Bahía Sebastián Vizcaíno, BC

Abstract

Hydrographic observations of currents and satellite images obtained from 7 to 19 September 1992 were used to analyze variability, on a time scale of days, of a anticyclonic eddy located in Bahía Sebastián Vizcaíno. The results indicate that during September 1992 there was a close relationship between the superficial manifestation of a warm-water eddy in the interior of Bahía Sebastián Vizcaíno and the intensification or relaxing of the upwelling to the north of the bay off Punta Baja. During episodes of intense wind from the northwest, the eddy was delimited by marked gradients of surface temperature, generated by the advection of low-temperature water that rose to the surface in Punta Baja and was transported towards the interior of the bay. During periods on the order of days, the diameter of the eddy fluctuated between 55 and 75 km and its depth between 40 and 55 m; these fluctuations were associated with variations in the wind intensity. A noteworthy characteristic of the wind field in the interior of the bay was the generation of a calm zone to the southwest of Isla de Cedros when winds from the northwest were present. The wind stress curl resulting from that distribution produces a convergence in the Ekman transport, which, according to the recent results of a barotropic model applied to Bahía Sebastián Vizcaíno (Palacios et al., in preparation), is the mechanism responsible for generating the anticyclonic eddy. The observations made indicate that there also exists an important baroclinic response to this convergence of the Ekman transport.