Three-dimensional aspects of the seasonal heat balance in the Gulf of California

Previously unresolved three-dimensional aspects of the time mean, as well a s the annual and semiannual cycles of the heat transport, ari studied in th e Gulf of California using a minimal box model suggested by the hydrographi c data. At the very least three horizontal domains are needed for the model a shallow region north of the big islands, a deep region identifiable with the Ballenas Channel, and another deep region spanning the rest of the gul f south of the archipelago. Only one vertical layer is considered in the no rthern region, whereas two layers are taken into account in the other two r egions. Out of all of the possible heat exchanges among the various boxes o f the model, the least-flux-variance solution is considered. The annual mea n heat entering the surface in the northern region is exported in almost eq ual amounts to the Ballenas Channel and the southern region. Ballenas Chann el, in turn, exports heat to the southern region mainly through the lower l ayer, producing a transversal asymmetry of the mouthward flux into the uppe r layer. At the mouth the heat is exported to the Pacific Ocean largely thr ough the upper layer. Both the annual and semiannual amplitude of the excha nges between all regions are as important as the annual average, except at the mouth of the gulf, where the semiannual component is not statistically relevant. The Pacific Ocean fluxes estimates at the annual frequency agree well with those produced by a baroclinic wave, which has been shown to expl ain a bit; deal of the thermodynamics of the gulf. The annual mean vertical flux per unit horizontal area in the Ballenas Channel is much larger than that in the southern region. This reinforces previous speculations that mix ing processes in this region are very important. A depth-independent eddy d iffusivity parameterization suggests that diffusion might not be invoked to explain the annual, mean vertical flux in the Ballenas Channel.