Observing the coastal ocean with HF radar

Graduation date: 2006Coastal-based high-frequency (HF) radar systems are an increasingly used tool for\ud measuring surface currents in the coastal ocean. These systems provide a spatial and\ud temporal resolution not achievable with other methods. Standard-range sites typically\ud generate hourly maps of surface currents on a 2km grid extending approximately 50km\ud from shore while long-range sites typically generate hourly maps on a 6km grid\ud extending up to 200km from shore. Generating these maps from the data presents\ud mapping challenges addressed in this thesis. The known geometric errors in HF radar\ud current maps are reviewed. Modifications to the traditional method of mapping coastalbased\ud HF radar measurements are proposed. One year of current data from the Oregon\ud coast and idealized radials representing different analytically-defined currents are used to\ud evaluate mapping issues, comparing the revised method with the traditional method. The\ud revised method showed improved accuracy, particularly in capturing small features.\ud The revised mapping method is applied to a deployment of two CODAR\ud standard-range HF radar sites from May 8, 1996 through May 22, 1996. The sites were\ud located at Bandon and Cape Blanco, Oregon. A nearby coastal wind station, an R/V\ud Wecoma research cruise, a mooring and satellite-tracked drifters provide additional\ud observations. Wind patterns during the study period included upwelling-favorable\ud conditions, a relaxation event, a weak reversal and a strong reversal. Analysis of the data\ud provides insight into coastal circulation during these varied wind conditions. The largescale\ud currents on the continental margin just north of Cape Blanco are wind-driven, with\ud a bias towards southward flow even when winds reverse to weakly northward. During a\ud wind relaxation event the coastal jet weakens with the area of maximum currents shifting\ud offshore. During a weak wind reversal event complex current patterns are observed\ud inshore of a weakened coastal jet. During a strong wind reversal event currents reverse to\ud northward and no coastal jet is observed. Drifter data and Lagrangian analysis of the HF\ud radar data early in this strong reversal are compatible with the theory of larval retention\ud in lee eddies and settlement north of a cape during a reversal event. Later in the reversal\ud event strong offshore flow develops at Cape Blanco which would prevent larval\ud settlement. The tides in the HF radar observation area are seen to be highly variable\ud spatially and of considerably greater magnitude than anticipated, potentially due to the\ud misallocation of the diurnal wind-forced currents to the diurnal tidal components