Periodic and aperiodic variations of temperature, humidity and water temperatur at the tropical Atlantic during ATEX

During the driftage of R. V. "Meteor" within the "Atlantic Trade Wind Experiment (ATEX) 1969" time series of wind velocity, air and sea temperature and humidity were measured on a buoy drifting windward of the disturbed zone of the ship. Using the profile method, vertical fluxes of momentum and sensible and latent heat were calculated. Time variations in the periodic range from 2.5 minutes to 5 days are analysed. Within the 18 days period the vertical fluxes of latent heat and momentum vary by a factor of 5 because of long period wind variations. For wind velocity, flux of momentum and flux of latent heat the variations in the range of periods greater than one day contribute most of spectral energy (65-85%) to total variance, while for air and water temperature, humidity and sensible heat flux the variations with periods smaller than one day represent more than 50% of total variance. For most of the mentioned variables the contribution of diurnal and semi-diurnal oscillations to total variance is small (3%), only for pressure, air and water temperature it is about 30% . The measurements during rain showers point out that even weak or moderate showers influence the surface layer right down to the sea surface. The amplitudes of the diurnal courses depends on the distance of the measurements to the air-sea interface. The diurnal course of water temperature follows the variation of incoming solar radiation, with increasing depth its amplitude is reduced and the phase is lagged. Applying the equation of diffusion to the diurnal harmonic water temperature oscillation down to 50 m depth, a coefficient of thermal diffusivity in water of K = 0.0525 - 0.00075 z (m2/s), decreasing with depth, was calculated. The diurnal variation of air temperature is influenced by the diurnal course of sea surface temperature. A semi-diurnal oscillation is superimposed by the semi-diurnal pressure wave because of adiabatic warming. The observed increase of the amplitude with height is caused by absorption of solar radiation. The stability of density stratification also shows a marked diurnal variation with a maximum of lability at night. This effects directly the variation of sensible heat flux. Humidity mainly shows a diurnal variation, the reason may be a diurnal variation of the divergence of vertical water vapor transport