A numerical study of the Lagrangian circulation in the Gulf of California

The advection of particles is studied numerically in order to obtain patterns of the Lagrangian circulation in the Gulf of California during the two major seasons in the gulf. A two-dimensional vertically integrated model is used to generate the velocity fields. The forcing agents are the principal lunar ride specified at the mouth of the gulf and wind stresses representative of summer and winter conditions. The flow geometry, i.e., the set of stagnation points and their associated streamlines, is computed for the mean velocity field of each season. These geometries show the well-known features of the gulf's surface circulation: A cyclonic gyre during summer (anticyclonic in winter) in the northern gulf; and a up-gulf coastal jet on the mainland side during summer (down-gulf in winter) in the southern gulf. It is shown that these mean-flow geometries govern the advection of the total velocity field for time scales much longer than the tidal period. The seasonal gyres of the northern gulf effectively trap particles for periods of up to two months. The along-shore flows of the southern gulf transport particles over hundreds of kilometers. northward in summer and southward in winter. (C) 1999 Elsevier Science B.V. All rights reserved.