Measurements of the Turbulent Fluxes of Momentum, Moisture and Sensible Heat over the Ocean

Abstract

This paper describes results of measurements of the fluxes of momentum, moisture and sensible heat by both the eddy correlation and “dissipation” techniques. The data were collected on the R/V Flip during BOMEX (Barbados Oceanographic and Meteorological Experiment) and during a pre-BOMEX trial cruise near San Diego in February 1969. The results are mainly based on data collected by personnel from Oregon State University and the University of British Columbia. We are grateful to the University of Washington personnel who have made their data and results available to us to check some of our results and allowed us to use their temperature fluctuation data from the San Diego cruise when our equipment failed to provide such data. The methods of determining the fluxes are discussed. The instrumentation and methods of data analysis are described. The effects of Flip's interference on the flow are described and the method of removing the interference from the results is given. The spectra of the three components of velocity fluctuations and the cospectra between the vertical velocity fluctuations w and the downstream velocity u, temperature T, and humidity q fluctuations are presented. The fluxes determined by the eddy correlation method are compared with fluxes estimated from the rates of dissipation of kinetic energy and scalar fluctuations. These fluxes are then used to evaluate the constants in the bulk aerodynamic formulas for estimating the fluxes. The normalized velocity component spectra and the normalized uw cospectra appear to have universal forms and are similar to earlier results. The normalized wT cospectra do not appear to have a universal form. The normalized wq cospectra do appear to have a universal form and are very similar to the normalized uw cospectra. As has been found before, the dissipation and eddy correlation methods agree quite well on the average for the momentum flux. The two methods do not give the same results for the sensible heat flux for BOMEX although there is fair agreement for the small number of San Diego results. The two methods do give good agreement for the moisture flux. Comparison of the eddy correlation flux for momentum with the mean wind speed squared leads to a drag coefficient of 1.5 × 10⁻³. The sensible heat flux, however, does not show a good relationship with the mean wind speed times the mean sea-air temperature difference during BOMEX. For the San Diego results the relationship is fair and similar to other measurements. The moisture flux shows a strong correlation with the wind speed times the mean sea-air humidity difference. The non-dimensional aerodynamic evaporation coefficient (corresponding to the drag coefficient for momentum) was found to be 1.2 × 10⁻³ with an uncertainty of about 20%. This result based on direct measurements of the flux agrees rather well with some earlier indirect estimates based on evaporation pan data.