Air–Sea Interaction on the Time Scale of 30 to 50 Days

In this Paper we have examined the fluxes of latent and sensible heat between the ocean and the atmosphere utilizing primarily the observations from the global experiment. The procedure for calculation is based on the Monin-Obukhov similarity theory. The transfer coefficients are stability dependent. Some calculations are also performed utilizing several different datasets. One of these covers the region of Asian monsoon oceans during the Global Experiment. This is a daily sea surface temperature (SST) dataset. A second dataset covers the global oceans for the entire FGGE year. This is a 10-day averaged dataset prepared by the European Centre for Medium Range Weather Forecasts. A third dataset obtained from the Japan Meteorological Agency, covers a 7-year period between 1979 and 1985. This dataset was also averaged over 10-day periods. Both the daily and the 10-day averaged SST data have been used for studies of low frequency oscillations. An equivalence, on the time scale of 30 to 50 days, for the oscillations of these two datasets is demonstrated. The global distribution of SST oscillations on this time scale are explored. The region of pronounced variance in the SST oscillation lies over the equatorial western Pacific Ocean and the Bay of Bengal. Calculations of air-sea energy fluxes include (i) the total contribution, (ii) those contributed on the time scale of 30 to 50 days, and (iii) those obtained by suppressing oscillations for one or more of the variables on this time scale. The main results of these computations show that SST oscillations with an amplitude of 0.3° to 1.0°C occur on this time scale over the tropical oceans. The fluxes of latent and sensible heat on this lime scale over the tropics have mean amplitudes of the order of 30 and 3 W m−2, respectively. The typical mean total fluxes in these regions are of the order of 200 and 30 W m−2 respectively. The fluctuations in the wind speed and the sea surface temperatures control the heat and moisture fluxes on the time scale of 30 to 50 days. Fluctuations of surface air temperature and surface humidity do not seem to be important over most oceans. Among these variables the role of the wind oscillations is somewhat larger. Proposals for further studies towards the understanding of oscillations on this time scale are presented.