Date of Award

2008

Degree Type

Thesis

Degree Name

Master of Science in Oceanography

Department

Oceanography

First Advisor

David Ullman

Abstract

The cross-shelf structure of fronts, which occur during the winter months along the 30 m and 50 m isobath, are examined using remote sensing observations of the southern New Jersey shelf region. Shipboard observations show that cooler, fresher, less dense water is located inshore of the front; however, little is known of the velocity structure in the frontal zone. Surface current fields from high-frequency radar are analyzed along with surface thermal front observations to describe the cross-shelf spatial variability of surface flow with regard to the fronts. Cloud-cleared, Level 2 MODIS Thermal IR sea-surface temperature (SST) data from AQUA and TERRA from winters 2003 - 2007 are processed using an edge-detection algorithm to determine the frequency, location, strength and orientation of the fronts. The record and seasonal progressions of the temperature and velocity fields are analyzed. No evidence is found to support the Ou Tidal Diffusivity theory that predicts that front location is a function of the spring-neap cycle. Cross-shelf locations of convergence due to the surface velocity appear to increase front occurrence, which is in agreement with Hoskins' frontogenesis theory. Shear/voriticity also seems to play a role in front occurrence and front orientation. Al so of note is that the location of minimum cross-shelf velocity variance is coincident with 30 m isobath fronts, while the minimum in along-shelf velocity variance is at the 50 m isobath. Furthermore, the 30 m (50 m) is the location at which the cross-shelf (along-shelf) wind-driven surface velocity component becomes greater (less) than the residual surface velocity component. Additionally, the front strength, measured by SST gradient magnitude, is inversely related to heat flux in the 50 m isobath region and nearly unrelated to the heat flux in the 30 m isobath region.

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