Surface dispersion in the Gulf of California

Abstract

Surface dispersion is measured in the Gulf of California by means of Argos drifters released along this semi-enclosed, elongated basin. First, basic one-particle statistics (Lagrangian scales, absolute dispersion and diffusion coefficients) are estimated along and across the Gulf. Absolute dispersion shows a nearly ballistic regime during the Lagrangian time scale (<2days) in both directions (it grows as ∼t2, where t is time). During the subsequent 30days, absolute dispersion enters a random-walk regime (∼t) along the Gulf, while being saturated across the basin due to the lateral boundaries. Secondly, the analysis is extended to two-particle statistics (relative dispersion between pairs of drifters and Finite Scale Lyapunov Exponents, FSLE). Relative dispersion is nearly exponential in both directions during the first few days, though evidence is not conclusive. During the subsequent 30days, it grows as ∼t1.5 along the Gulf, while being saturated across the basin again. It is shown that relative dispersion along the Gulf is proportional to t̂3, where t̂ represents a shifted time that depends on the initial separation of the particles. This form of the Richardson regime is consistently measured for particles that are sufficiently separated (30km or more). The Richardson regime is verified with the FSLE for particle separations ranging from 30 to 140km, approximately. The obtained dispersion properties are discussed in terms of the main circulation features within the basin, such as mesoscale vortices that occupy the width of the Gulf. These structures might retain buoys during days or weeks, thus preventing or delaying further displacements and therefore affecting the particle dispersion. The vortices are also an important mechanism to translate particles across the Gulf, between the Peninsula and the continent, thus promoting the saturation of dispersion along this direction.