Toward a Physical Explanation of the Seasonal Dynamics and Thermodynamicsof the Gulf of California

Abstract

The annual component of the horizontal heat flux Fx is calculated from the temperature advection by the geostrophic velocity. This estimate of Fx is in good agreement, in amplitude and phase and as a function of the distance x to the head, with that calculated from the difference between the surface heat flux Q and the local heating, that is, from ?Fx/?x = Q ? ?H/?t, where H denotes the heat content. Sea level ? variations are well correlated with those of H, while the surface velocity usurf (which can be calculated from the difference of ? between both coasts) is well correlated with Fx. The proportionality coefficients between (?, H) and between (usurf, Fx) correspond to what is expected for a dominance of the first baroclinic mode, in spite of the inhomogeneity of the gulf?s topography. A linear one-dimensional two-layer model is enough to reproduce the observations of the transversely averaged (?, H, usurf, Fx) fields at the annual frequency. Most of the dynamics and thermodynamics are controlled by the Pacific Ocean, which excites a baroclinic Kelvin wave at the mouth of the gulf. Wind drag produces a slight slope in ?, whereas Q causes a local heating of the upper layer; both surface forcings have a small effect on usurf and Fx.