Observations of a coastal buoyant jet with HF Doppler radar

Abstract

Currents on the inner shelf respond to a combination of forcing by intrusions of ocean fronts, eddies and internal waves as well as winds, surface gravity waves and topographic rectifications. To quantify the effect that the interaction of these processes has on inner shelf flows, a shore-based, 25.4 MHz (High Frequency) Ocean Surface Current Radar (OSCR), operated by the Radar Ocean Sensing Laboratory (ROSL) of the University of Miami, was deployed to measure the surface current vector field at high spatial and temporal resolution over the inner and mid shelf. Surface currents were mapped in near-real time over a domain bounded in the south by the US Army Waterways Experiment Station's Field Research Facility along the central mooring array of the Coastal Ocean Processes (CoOP) shelf experiment and extended about 27 km northward to include two additional CoOP transects. The surface current vectors were measured at a spatial resolution of about 1 km every 20 minutes during October 1994. Over the experimental period of about 30 days, quality data were acquired 96% of the time extending to the maximum theoretical range of 44 km. Time series or the surface current vectors were in close agreement with near-surface measurements from moored current meters. The surface current maps revealed numerous surface current features. One such feature was the buoyant coastal jet formed by the Chesapeake Bay outflow. A five day period when the buoyant jet was evident in the OSCR generated surface current maps is described to demonstrate the capabilities of HF radar to infer dynamical properties of coastal flow features from measured velocity fields.