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- Title
Current Structure Variations Detected by High-Frequency Radar and Vector-Measuring Current Meters.
- Authors
Shay, Lynn K.; Lentz, Steven J.; Graber, Hans C.; Haus, Brian K.
- Abstract
Ocean surface current measurements from high-frequency (HF) radar are assessed by comparing these data to near-surface current observations from 1 to 30 October 1994 at two moored subsurface current meter arrays (20 and 25 m) instrumented with vector-measuring current meters (VMCMs) and Seacat sensors during the Duck94 experiment. A dual-station ocean surface current radar (OSCR) mapped the current fields at 20-min intervals at a horizontal resolution of 1.2 km over a 25 km 3 44 km domain using the HF(25.4 MHz) mode and directly overlooked these moorings. In response to wind, tidal, and buoyancy forcing over 29 days, surface current observations were acquired 95% of the time in the core of the OSCR domain, decreasing to levels of about 50% in the offshore direction. Regression analyses between surface and subsurface measurements at 4 and 6 m indicated biases of 2--6 cm s[sup-1], slopes of O(1), and rms differences of 7--9 cm s[sup-1] . Episodic freshwater intrusions of about 30 practical salinity units (psu) were associated with a coastally trapped buoyant jet superposed on tidal currents. This tidal forcing consisted of diurnal (K1 ) and semidiurnal (M2 ) tidal constituents where the surface and subsurface (4 m) speeds were 3 and 8 cm s[sup-1] ,and 2 and 7 cm s[sup-1] , respectively. During the passage of a nor'easter, near-surface winds reached 14 m s[sup-1] , which induced vertical mixing that caused weak stratification in the water column. An abrupt wind change following this event excited near-inertial (~20.3 h) currents with amplitudes of about 20 cm s[sup-1] rotating clockwise with time and depth. Bulk current shears over 4- and 6-m layers were O(10[sup-2] s[sup-1] ) at the 25-m mooring where the correlation coefficients exceeded 0.8. Similar results were found at the 20-m mooring until the nor'easter when correlation coefficients decreased to 0.5 due to the superposition of storm-induced flows and the buoyant jet, causing the (...).
- Subjects
OCEAN currents; RADAR; FLOW meters; WATER current meters; MEASUREMENT
- Publication
Journal of Atmospheric & Oceanic Technology, 1998, Vol 15, Issue 1, p237
- ISSN
0739-0572
- Publication type
Article
- DOI
10.1175/1520-0426(1998)015<0237:CSVDBH>2.0.CO;2