The spectral density technique for the determination of eddy fluxes

The determination of turbulent fluxes from measurements of spectral densities of velocity, temperature and humidity is discussed as a technique applicable to the open ocean. A preliminary investigation over land using specially designed equipment measuring spectral densities of wind and temperature at a single frequency indicates that present understanding of the Kolmogorov and flux/gradient relationships is adequate for the purpose. Although humidity spectra are included in the treatment, no measurements of them were made. Values of the effective Kolmogorov constants for velocity and temperature are found to be 0.54 ± 0.03 and 0.71 ± 0.04 respectively, in good agreement with other recent determinations. The principles of application of the technique at sea are discussed. The method assumes that the divergences of the eddy energy fluxes can be neglected. Whilst the present results appear to support this assumption, there is a need for further examination of this aspect.