LAGRANGIAN OBSERVATIONS OF THE CIRCULATION IN THE NORTHERN GULF OF CALIFORNIA

ARGOS drifters deployed in the Northern Gulf of California in Septembe r 1995 showed the presence of a cyclonic gyre, while a second deployme nt in March 1996 revealed an anticyclonic gyre. A circulation pattern consisting of a seasonally reversing gyre had been proposed before on the basis of satellite images, geostrophic calculations, and numerical models, but so far no direct observations have been made to test its existence. In September the gyre was cyclonic, baroclinic, very well d efined, stable, and strong: its mean speed and rotation lime were 0.3 m s(-1) and similar to 7 days. In March the gyre had the same mean spe ed, but it was anticyclonic and displaced to the northwest of the summ er position The March gyre has barotopic and baroclinic characteristic s, but the observed speeds are stronger than in numerical simulations, These dare and a data bank analysis suggest that the summer gyre is a persistent summer feature, but the winter-spring situation remains il l-defined and requires further research.