A Field Evaluation of NDBC Moored Buoy Winds

Abstract

Several field intercomparisons of buoy winds were conducted to investigate the quality of the observations. Differences between dual anemometers on the same buoy were calculated during tropical cyclones. The speed and direction differences did not grow appreciably with increasing wind speed, and at no time was the speed difference greater than 1 m s⁻¹. Differences between winds measured at colocated buoys and a buoy moored near a platform were investigated. Standard deviations of speed differences were less than 1 m s⁻¹ and direction differences were less than 11°. The differences were slightly larger in certain sea stares in the interbuoy comparison. No similar evidence was found when buoy winds were compared to platform winds. Several comparisons were conducted to help quantify errors that arise when buoy winds are used as comparison data for satellite-based scatterometer and altimeter winds. First, 8.5 min average winds were compared to hourly average winds to investigate effects introduced by the buoy's short averaging period. Second, speed and direction differences between pairs of buoys located 39 and 109 km apart were calculated to determine differences due to spatial variation in the wind field. Differences due to spatial variations were larger than differences introduced by the short averaging period. Therefore, researchers are urged to compare remotely sensed winds with buoy winds only when the distance between the center of the footprint and the buoy is considerably less than 100 km.