Free convection frequency spectra of atmospheric turbulence over the sea

Frequency spectra of atmospheric turbulenceS α (f) in the inertial subrange are considered in the free convection regime over the sea surface in a case of motionless instrument measurements (Eulerian frequency spectra). The frequency spectra formulaef * S α(f)/σ α 2 =c α(f */f)5/3 for wind velocity (α=1–3), temperature (α=t) and humidity (α=e) fluctuations are derived on the basis of similarity theory and the “−5/3 law”. These relations also can be derived from a consideration of convective large-scale advection of small eddies. The frequency scalef * = (N 1 β 2/∈)1/2 ≈ (βH/z 2)1/3 is the lower bound of the inertial subrange and it is of order 10−2 Hz. The spectra formulae are compared with direct measurements of atmospheric turbulence from the fixed research tower in the coastal zone of the Black Sea in calm weather. It is shown that these formulae are realized at least over two to three decades of the frequency range (approximately from 10−2 to 10 Hz) and values of the numerical coefficients are found. The derived formulae can be used for calculations of sensible and latent heat fluxes by measuring the high-frequency range of spectra at a fixed point at low wind speeds when the conventional inertial dissipation method is not applicable.