Barotropic background currents in the Gulf of California

Abstract

A field of barotropic background currents (BC) in the Gulf of California is constructed numerically. The definition of BC used here is based on suppositions about (i) the horizontal homogenization of potential vorticity in large-scale gyres, and (ii) the tendency of a current structure to evolve to a state with a minimum of system mechanical energy. In the barotropic case here, the numerical algorithm is reduced to the solution of the Dirichlet boundary problems for planetary, topographic and flowing integral streamfunction components separately. The results obtained are compared to observations and the results of other numerical models. The calculated barotropic BC realistically describe the main features of the circulation in the southern part of the Gulf of California, including its mouth. Cyclonic movement in the deep-water and anticyclonic movement near the coasts are observed. The numerical results for the central and northern parts of the gulf, where seasonal climatological differences are pronounced, coincide with observations in the upper layer only during the winter season; i.e., the circulation here is anticyclonic. Thus, there are reasons to suggest that mainly planetary-topographic forcing, especially in the southern part, forms the circulation in the lower layer. The seasonal variability of currents in the upper layer caused by non-stationary effects such as wind, heat flux and baroclinicity, is apparently in phase with these mechanisms during winter, and in antiphase during summer, particularly for the central and northern gulf.