Modeled wind-driven flow over the California continental shelf in terms of a local and a remote response

• Other Authors: Lopez, Manuel.
• Format: Others
• Language: English
• Subjects: Physical Oceanography
• Online Access: http://purl.flvc.org/fsu/lib/digcoll/etd/3161934

Previous results suggest that many higher order coastally trapped wave (CTW) modes are needed to calculate the low-frequency wind-driven alongshore flow over the continental shelf. Large mode number CTW asymptotics suggest that the higher order modes are generated by just the local wind. It is therefore convenient to regard the velocity field as being due to a two dimensional "local" solution driven by local winds and a "remote" solution driven by the alongshore pressure gradient and depending on nonlocal wind stress. The alongshore pressure gradient can be accurately estimated using the lower order CTW modes and the "Local Plus Remote" solution can easily be obtained at a given coastal cross section. Tests using a simple sinusoidal wind forcing and realistic parameters for two different shelves show that the Local Plus Remote (LPR) method can accurately estimate the alongshore flow with the alongshore pressure gradient estimated with only 3 modes. The CTW method fails to accurately represent the alongshore flow field when even 6 modes are used. === The LPR method was applied to the Coastal Ocean Dynamics Experiment (CODE) shelf using realistic winds and the modeled alongshore velocities were compared with observations. In this application a background mean density field with sloping isopycnals and the wind stress curl were also included under the assumption that they are only important to the local part of the solution. Tests using a simple sinusoidal wind forcing confirm that this assumption is reasonable for velocity fields driven predominantly by local winds. The comparison with observed and CTW modeled velocities shows that the higher order modes, the mean density field with sloping isopycnals and the wind stress curl all have an effect on the amplitude and structure of the alongshore flow. The wind stress curl causes significant vertical shear in the inner and mid shelf and this shear compares well with that observed. A simple model for nearly barotropic flow shows that a wind stress with amplitude increasing offshore but with negative curvature (i.e., ($\tau\sb{\rm o}$)$\sb{\rm xx}$ $<$ 0), as observed during CODE, will produce surface intensification of the alongshore flow. Separation of the total modeled response into local and remote components reveals that the wind-driven response during both CODE periods was predominantly driven by local winds on the inner and mid shelf, but it was equally local and remote on the outer shelf. === Source: Dissertation Abstracts International, Volume: 50-12, Section: B, page: 5525. === Major Professor: Allan J. Clarke. === Thesis (Ph.D.)--The Florida State University, 1989.