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  • Author or Editor: Clinton D. Winant x
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Sabine Harms and Clinton D. Winant

Abstract

Synthetic subsurface pressure (SSP) can be formed from tide gauge records and from bottom pressure measurements to provide a consistent and convenient basis for comparison of these two different types of observations. Common methods for this estimation are reviewed, and their accuracy is evaluated. Calculations show that subtidal SSP estimates from sea level (SSPSL) and from bottom pressure observations (SSPBP) at close sites agree only in a finite band of frequencies, corresponding to periods between 3.5 and 30 days. At the lower frequencies (periods longer than 30 days), sea level observations are subject to errors induced by the daily measure of staff height. At higher frequencies (periods between 1.5 and 3.5 days), the amplitude of fluctuations is too small to be resolved by a sea level gauge.

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Paul A. Spyers-Duran and Clinton D. Winant

Abstract

A comparison of sea surface temperatures is made between aircraft precision radiation thermometer (PRT-5) and aircraft deployed expendable bathythermographs (AXBT) drops. These observations were obtained using the NCAR King Air aircraft for an experiment in the Gulf of California during March 1984. The average difference between the sea surface temperatures reported by the first temperature observed in each AXBT drop and the PRT-5 is −0.07°C with a standard deviation of 0.57°C. The difference in temperature between the two observations increases at lower wind speeds. Based on 116 case studies, differences of 1–2°C exist between the surface and the upper meter of the ocean when wind speeds are less than 5 m s−1.

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Carl A. Friehe, Robert C. Beardsley, Clinton D. Winant, and Jerome P. Dean

Abstract

Intercomparisons of meteorological data—wind speed and direction, surface temperature and surface pressure—were obtained for NCAR Queen Air overflights of four buoys during the CODE-1 experiment. The overflights were at a nominal altitude of 33 m. Wind and air temperature sensors were at 10 m on two National Data Buoy Office (NDBO) buoys and at 3.5 m on two Woods Hole Oceanographic Institution (WHOI) buoys. The buoy wind speeds were adjusted to the aircraft altitude using diabatic flux-profile relations and bulk aerodynamic formulas to estimate the surface fluxes and stability. For the experimental period (22 April-23 May 1981) and location (northern coast of California), the atmospheric surface layer was generally stable, with the Monin-Obukhov length on average 500 m with large variability.

The results of the intercomparisons of the above variables were in general good. Average differences (aircraft - buoy) and standard deviations were +0.1 m s−1 (±1.8) for wind speed, 3.3 deg (±11.2) for wind direction, +0.02°C (±1.7) for air temperature and +0.8 mb (+1.0) for surface pressure. The aircraft downward-looking infrared radiometer indicated a surface temperature 1°C lower than the buoy hull (NDBO) and 1 m immersion (WHOI) sea temperature sensors.

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Andreas Münchow, Charles S. Coughran, Myrl C. Hendershott, and Clinton D. Winant

Abstract

A towed acoustic Doppler current profiler (ADCP) system was tested. The instrument was deployed from ships of opportunity and towed at depths between 5 and 25 m. The towed system carries upward- and downward-looking ADCPs. The instrument platform is stable in most operating conditions at ship speeds up to 4.5 m s−1. Large discrepancies are found, however, between the ship's velocity obtained from bottom-tracking ADCP pulses and that from navigational data. These are explained with a magnetic compass bias that varies with the ship's heading direction. Both the ship and the tow platform induce magnetic fields that bias the ADCP compass. An in situ compass calibration scheme is thus necessary and requires accurate navigational data. In our main study area, it is found that the Global Position System provides absolute and relative positions to within 88 and 4 m, respectively. These accuracies are sufficient for calibration purposes. With our calibration scheme the towed ADCP system performs as well as vessel-mounted systems. The case of deployment from ships of opportunity and the capacity of the tow system to carry additional instruments makes it a valuable research tool. Furthermore, the capability of our system to profile the water column above and below the platform with different frequencies and thus different vertical resolutions enhances its flexibility and usefulness, especially to study surface and bottom boundary-layer processes.

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