National Data Buoy Center Buoy Research Articles

The Spring 1998 Northeastern Gulf of Mexico (NEGOM) Cold Water Event: Remote Sensing Evidence for Upwelling and for Eastward Advection of Mississippi Water (or: How an Errant Loop Current Anticyclone Took the NEGOM for a Spin)

Temperatures of coastal waters along the Florida Panhandle in the northeastern Gulf of Mexico were 2-6 C lower in May-July 1998 than is normal for these waters at this time of the year. Surface temperatures were up to 7 C colder than air temperatures measured nearby off Alabama at National Data Buoy Center (NDBC) buoy 42007. Satellite data from the Advanced Very High Resolution Radiometer, Sea-viewing Wide-Field-of-View Sensor, the Ocean Topography Experiment, and European Remote-sensing Satellites altimeter sensors were combined with wind, air temperature, and water temperature data gathered at NDBC buoys to document the anomalous wind, temperature, and river plume dispersal patterns. The difference between the water and air temperatures suggests that upwelling caused the cooling of coastal waters. Eastward, upwelling-favorable winds stronger than 3 m·s-1 occurred along the Alabama coast up to 32% of the time between May and August 1998 compared with only about 20-26% during the same months in 1996, 1997, and 1999. The altimeter data suggested that a large anticyclonic eddy migrated far into the northeastern Gulf of Mexico, interacting with shelf waters through August 1998. Upwelling was probably enhanced by the presence of baroclinic structure associated with the eddy. The eddy contributed also to convergence near the Mississippi River Delta, eastward flow along the coast, and offshore flow in the region between Fort Walton Beach and Cape San Bias, FL. The region experienced anomalously high river discharge during this period as a result of increased precipitation over northern Florida (a teleconnection to El Niño of 1997-1998), and further, turbid Mississippi River water dispersed eastward along the coast. Decay of local phytoplankton blooms off northern Florida in late June and early July 1998 probably followed after eastward winds relaxed, westward winds increased, and low-salinity waters led to vertical stability in the water column, possibly leading to hypoxia along these shores.

Error analysis of the directional wave spectra obtained by the NDBC 3-m pitch-roll discus buoy

The National Data Buoy Center (NDBC) deploys a series of 3-m-diameter discus directional wave buoys around the coastline of the United States and its territories. These buoys make available a continuous set of hourly wind and directional wave data. This study estimates the accuracy of the significant sea height, mean sea direction, and the full directional wave spectrum, which are the major wave data parameters commonly derived from the NDBC buoy measurements. The errors are examined both on the basis of the uncertainty inherent in deriving results from the measurement of a random sea and through a statistical examination of a select section of data from a specific buoy. The errors in the derived parameters are found to be quite small, less than 3% in the sea height and usually less than 4/spl deg/ in the peak wave direction. However, errors in the directional wave spectra are found to be potentially significant. These errors are associated with the buoys only measuring sufficient data for the first two terms of the Fourier expansion of the directional spectrum. This measurement limitation is due to the operational requirements of the buoys and not due to any defects or design flaws. This limitation is examined in terms of its effect on the accuracy of the derived wave spectra. A method is developed in this study which allows for a maximum error estimate to be calculated for each hourly record of the buoy data with the goal of guiding the selection of those records which meet the accuracy requirements of a particular application utilizing the data. A select set of NDBC data, consisting of 1369 hourly records collected by Buoy 44 014 during August and September 1993, are analyzed to provide an overview of the size and variety of this error source of the measured directional spectrum. It is found that approximately 60% of the sample wave records give an upper bound rms error of less than 30% of the rms energy of the spectrum, which may be sufficiently accurate for many research requirements.

A Comparison of Directional Buoy and Fixed Platform Measurements Of Pacific Swell

The performance of the Datawell Directional Waverider and the National Data Buoy Center (NDBC) 3-m discus buoy, widely used to measure the directional properties of surface gravity waves, are evaluated through comparisons to an array of six pressure transducers mounted 14 m below the sea surface on a platform in 200-m depth. Each buoy was deployed for several months within a few kilometers of the platform. The accuracy of the platform ground-truth array was verified by close agreement of wavenumber estimates with the theoretical linear dispersion relation for surface gravity waves. Buoy and array estimates of wave energy and directional parameters, based on integration of the directional moments across the frequency band of energetic swell (0.06–0.14 Hz), are compared for a wide range of wave conditions. Wave energy and mean propagation direction estimates from both buoys agree well with the platform results. However, the Datawell buoy provides significantly better estimates of directional spread and skewness than the NDBC buoy.

Comparison of Buoy-Mounted 75-kHz Acoustic Doppler Current Profilers with Vector-Measuring Current Meters

Abstract Long time series of atmospheric parameters and limited oceanographic parameters such as near-surface temperature and wave statistics have been available for some time. There is, however, a need for similar observations of currents in the coastal ocean. In December 1991, the National Data Buoy Center (NDBC) deployed two meteorological buoys in the Southern California Bight on a transect between San Diego and San Clemente Island. Each buoy consisted of a 10-m discus hull instrumented to measure a suite of meteorological parameters, and, for the first time in the NDBC buoy program, acoustic Doppler current profilers (ADCPs) were included to gather hourly current profiles beneath the two buoys. Moorings instrumented with seven vector-measuring current meters (VMCMs) were deployed adjacent to the NDBC buoys for several months and provided current observations for comparison with the ADCP measurements. When the situation is such that the wave-induced buoy motion is not overly large, the observations of...