Shipboard Turbulence Measurements of the Marine Atmospheric Boundary Layers From HiRes Experiment

Turbulence data were collected during the High Resolution Air-Sea-Wave Interaction (HiRes) main experiment aboard R/V Gordon Sproul from 1 to 30 June, 2010 offshore of Bodega Bay, California. Although two sets of measurements were made from the bow mast and the ship center mast, data from the bow mast were used because this position was found to be least affected by flow distortion due to the ship superstructure. Combined with in situ wave measurements, the sea-state dependent surface flux parameterizations were studied using this dataset by examining the effects of wind sea waves on turbulent transfer coefficients through the velocity roughness length. A comparison of various parameterizations showed that the formulation based on wave steepness fits the current dataset the best. Also, young wind sea waves as well as swell corresponded to high drag coefficients which are not explained by the existing parameterizations. Forecasts of the Coupled Ocean Atmospheric Mesoscale Prediction System (COAMPS) at the position of the ship were also compared with measurements and showed reasonable agreement for wind speed, wind direction, and friction velocity. The discrepancies between the forecast and observed differences in friction velocity were mainly due to the corresponding differences in wind speeds. The concurrent sodar measurements showed the existence of turbulence structures up to 250 m above sea level and the sodar estimated wind and momentum flux followed qualitatively the variations of mast data.