Spectra and Fluxes in the Boundary Layer of The Trade-Wind Zone

Abstract

From airborne turbulence measurements in the lowest 500 m of the atmosphere over the tropical Atlantic east of the island of Barbados, various characteristics of the turbulent boundary layer are examined. The height dependences of the fluxes of momentum, moisture and sensible heat, and the intensity of the fluctuations of temperature, humidity and the velocity components are considered in both time and wavenumber domains. Many of the characteristics of the trade-wind boundary layer are thus revealed and related to the mean vertical distributions of temperature and humidity. Two of these characteristics are: The spectral shapes of the momentum and moisture fluxes are similar, containing contributions of the same sign from large and small scales alike. On the other hand, the sensible heat flux is upward at small scales and downward at large ones. Fluctuations of both temperature and humidity are less intense near an altitude of 150 m than they are above and below.