Height dependence of diurnal variations of wind velocity and water temperature near the air-sea interface of the tropical Atlantic

From measurements during the ‘Atlantic Trade Wind Experiment (ATEX) 1969,’ amplitudes and phases of the diurnal harmonic water-temperature variation between the sea surface and 50-m depth and of the semi-diurnal wind variation between 1 and 8 m were obtained. If the vertical diffusion of heat in the ocean is thought to be constant, a coefficient of K= 320 cm2 s−1 in the equation of diffusion fits best the observed data in the mixed layer. However, the measurements point to a decrease of K with depth. The height variation of the semi-diurnal zonal wind wave is caused by the influence of eddy viscosity. Our data are well fitted by results of the equation of diffusion, using the assumption of Lettau (1974) that the transfer coefficient of vertical transport of momentum is not only a function of height but also depends on time because of the semi-diurnal variation of surface stress.