Wind-Driven Subinertial Circulation inside a Semienclosed Bay in the Gulf of California

Abstract

oored current and pressure observations were obtained at Bahía Concepción, a semienclosed bay located on the eastern side of the Baja California peninsula in Mexico, to describe the wind-driven subinertial circulation. In winter and early spring, the bay is well mixed and forced by persistent winds toward the southeast, aligned with the central axis. The authors? observations show that the sea surface rises downwind in response to wind stress and that there exists a crosswind drift at the surface that is consistent with Ekman dynamics. This feature is typical of a bay that is deeper than one Ekman depth and hence affected by the rotation of the earth. There is a persistent along-bay circulation toward the end of the bay along its western side with return flow on the opposite side. Drifters released near the surface across a transect move westward and downwind toward the closed end, where they recirculate cyclonically. Wind-driven linear theoretical models successfully predict the observed cross-bay circulation but fail to predict the along-bay flow pattern. The role of spatial inhomogeneities of wind stress (suggested by synoptic observations of the wind) and nonlinearities related to advection of momentum is investigated with theoretical and numerical modeling. Both mechanisms can contribute to the observed pattern of along-bay circulation. Even though the observations discussed were taken during the relatively well-mixed season, density fluctuations are shown to play, at times, an active role dynamically.