Relative Dispersion Over the Inner Shelf: Wave Forcing, Anisotropy and Variations with Offshore Distance

Carter Ohlmann1, Leonel Romero2, Enric Pallas Sanz3 and Paula Perez-Brunius3, (1)University of California Santa Barbara, Earth Research Institute, Santa Barbara, United States, (2)University of California Santa Barbara, Earth Research Institute, Santa Barbara, CA, United States, (3)Center for Scientific Research and Higher Education at Ensenada, Physical Oceanography, Ensenada, BJ, Mexico
Abstract:
Lagrangian observations of near-surface relative dispersion, made coincidently with dye and drifters over the inner-shelf in the Gulf of Mexico, are presented. Dye evolution is tracked by an airborne remote sensing system that includes a hyperspectral irradiance sensor and a lidar to measure directional wavenumber spectra of surface waves. The Lagrangian observations, collected at locations between 2 and 12 km from the shore, resolve space scales ranging from ~0.1 to 1 km and time scales of a few hours. Relative dispersion growth, or eddy diffusivity, for the targeted scales is O(1 m^2/s). The dispersion is weakly anisotropic in a coordinate system aligned with bathymetry, but highly anisotropic in a principle axis coordinate system. Both submesoscale flows (associated with cross-shelf density gradients due to freshwater runoff) and Langmuir circulation drive the observed dispersion. Langmuir circulation identified in dye concentration maps contributes to the observed relative dispersion on almost all sampling days. Dispersion associated with density fronts is generally largest in the along-front direction (often with negative dispersion in the cross-front direction). Dispersion associated with Langmuir circulation is generally largest in the cross-wind direction.