Comparison of Surface Meteorological Observations from Ship and Toroid Buoy in the North Pacific During STREX

Abstract

Moored-buoy wind measurements were made at 20 min intervals at 3.4 m height at 50°8?N, 140°25?W in the North Pacific from 10 November to 12 December 1981. The measurements were part of the Storm Transfer and Response Experiment (STREX). The NOAA ship Oceanographer deployed the buoy and stood by within 25 km of it for an accumulated time of two weeks. The buoy measured wind by a vector averaging technique whereby the anemometer speed, compass angle and vane angle were combined at a 100 Hz rate. The averaging period was 640 s. The Oceanographer made standard ship observations with wind speed rounded to ±1 kt and direction rounded to the nearest 10°. Air and sea temperatures were used to correct all measurements to a standard height of 10 m with a diabatic surface layer model. The differences (ship - buoy) in wind speed and direction were compared. For wind speed, a mean difference of 0.8 m s?1 and standard deviation of 1.2 m s?1 was observed. For direction, a mean difference of 3.5° and standard deviation of 11° was observed. Differences were well correlated with ambient wind speed. The speed difference increased with increasing wind speed. This was particularly severe when the boundary layer was stratified, and could be related to streamline crowding over the ship. The absolute direction difference was less in higher winds, which is partly explained by increased variability in light-wind conditions.