The Effect of the Seasonal Variation of Stratification on the Circulation of the Northern Gulf of California

Direct current measurements reveal that the circulation of the northern Gulf of California in the annual timescale consists of a cyclonic basinwide gyre (∼0.35 m s−1) that lasts from June to September (4 months), and an anticyclonic gyre (∼0.35 m s−1) lasting from November to April (6 months). The transitions between regimes take about three weeks each. The hypothesis that the difference in duration of the two circulation regimes is due to the seasonal variation of stratification of the water column is explored by simulations with a nonlinear two-layer numerical model of circulation and thermodynamics that includes vertical mixing, parameterized as an entrainment velocity. The model results agree remarkably well with the observations, considering its simplified vertical structure. In addition, the model predicts a net circulation consisting of an anticyclonic gyre of ∼0.05 m s−1, with a corresponding average concavity of the interface, and a two-layer exchange through the main channels of the archipelago.