| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1998 This thesis is written in two parts. The first part deals with the problem oflateral dispersion due to mesoscale eddies in the open ocean, and the interaction between the mesoscale strain and horizontal diffusion on spatial scales less than 10 km. The second and major part examines lateral dispersion over the continental shelf on scales of 100 m to 10 km and over time scales of 1- 5 days. PART I: Lateral Dispersion and the North Atlantic Tracer Release Experiment Mixing and stirring of Lagrangian particles and a passive tracer were studied by comparison of float and tracer observations from the North Atlantic Tracer Release Experiment. Statistics computed from the NATRE floats were found to be similar to those estimated by Ledwell et al. (1998) from the tracer dispersion. Mean velocities computed from the floats were (u, v) = ( -1.2±0.3, -0.9±0.2) em s-1 for the (zonal, meridional) components, and large-scale effective eddy diffusivities were (KP. 11 , K:e 22 ) = (1.5±0. 7, 0. 7±0.4) x 103 m2 s-1 . The NATRE observations were used to evaluate theoretical models of tracer and particle dispersal. The tracer dispersion observed by Ledwell et al. (1998) was consistent with an exponential growth phase for about the first 6 months and a linear growth at larger times. A numerical model of mesoscale turbulence that was calibrated with float statistics also showed an exponential growth phase of tracer and a reduced growth for longer times. Numerical results further show that Garrett's (1983) theory, relating the effective small-scale diffusivity to the rms strain rate and tracer streak width, requires a scale factor of 2 when the observed growth rate of streak length is used as a measure of the strain rate. This scale factor will be different for different measures of the strain rate, and may also be affected by temporal and ...
|
|---|