TIDAL DISSIPATION AND STRATIFICATION IN THE GULF OF CALIFORNIA

The effect of tidal mixing upon the distribution of stratification and sea surface temperature (SST) in the Gulf of California is studied by direct observation and by numerical modeling. Data from conductivity- temperature-depth surveys made in September and December of 1986 are u sed to describe the distribution of stratification and SST. A vertical ly integrated finite differences numerical model was used to obtain th e geographical distribution of available turbulent kinetic energy (TKE ) from the Ma tide. The following three areas were found to be strongl y affected by tidal mixing: the shallow coastal area at the head of th e gulf, the shelf south of Tiburon island, and the area of the midgulf archipelago. The first two are vertically well mixed and are therefor e similar to other shelf sea frontal areas. Dissipation occurs all aro und the islands of the archipelago, and the sills are foci of the most intense tidal dissipation. Stratification in this area was reduced wi th respect to the background, but complete vertical mixing does not oc cur. Therefore the strong SST fronts that orrur in this area do not ma rk the boundary between well-mixed and stratified water. The Simpson-H unter criterion (Simpson and Hunter, 1974) for stratification and fron tal position [lambda = log(10)(h/(U-3) over bar)] produced 2.75 less t han or equal to lambda(crit) less than or equal to 3.0 for the frontal position in the shallow northern gulf. This value of lambda(crit) is larger than in other shelf sea fronts, which may be due to horizontal advection, which is not included in the criterion. We found that the e ffect of advection may be of the same order of magnitude as that of bu oyancy flux. In the area over the sills, lambda > lambda(crit), the av ailable TKE is not enough to produce complete mixing over the similar to 400 m of water over the sills.