Josh Kohut PhD Thesis - June, 2002

Spatial Current Structure Observed With a Calibrated HF Radar System:
The Influence of Local Forcing, Stratification, and Topography on the Inner Shelf

Click Here to download the Microsoft PowerPoint version of Dr. Kohut's dissertation defense.

Click Here to download Dr. kohut's thesis dissertation. It is approximately 1.2 MB.

Abstract


Ocean current variability over the inner shelf is presented here using an HF radar system. The system uses radio waves scattered off the ocean to measure the range, bearing and radial velocity of the scattering surface. For this particular system, the signal bearing is determined using the patterns of three independent antennas. A series of antenna measurements show that these patterns are often distorted when an antenna is deployed in the field. Based on these measured patterns, the local environment is identified as a significant contributor to the distortion. ADCP correlation indicates that data calibrated with the measured pattern are more accurate than the uncalibrated data. It is also shown that the error associated with the distorted patterns is due to incorrect estimates of the bearing toward the scattering surface.
The calibrated spatial time series data of the HF radar system is then applied to the inner-shelf circulation. The hydrographic variability of the inner shelf off New Jersey is largely bimodal between summer stratification and winter mixing. An annual oceanographic and atmospheric dataset was separated into these two regimes. The influence of stratification is evident through a relatively steady current response strongly correlated with the wind during the stratified season, and a more variable response less correlated with the wind during the mixed season. When the water column is mixed, topography orients the unstratified variability along the coast with spatial structure related to the local topographic slope.
The passing of tropical storm Floyd through the HF radar field offers a unique dataset for characterizing the inner shelf response to shorter time-scale forcing. Prior to the tropical storm, the water column was mixed leading to a barotropic response. This response is rectilinear in the along-shore direction and driven by a sea surface perturbation. This perturbation, setup by the storm surge and cross-shore winds, propagates through the study site, driving an oscillating along-shore response. Bottom friction is shown to quickly dissipate the energy associated with the episodic event.