A method of determining ocean-atmosphere moisture and latent heat fluxes using spaceborne sensors is presented and evaluated. The satellite data used are the geophysical parameters: sea surface temperature, precipitable water, and surface wind speed, derived from observations of the microwave radiometer on the Nimbus 7 spacecraft from 1980 to 1983 in the tropical Pacific. The period included one of the most intense El Ni¿o--Southern Oscillation (ENSO) episodes of this century. The surface humidity is first derived from the precipitable water using a global empirical relation and is found to be in close agreement with in situ measurements in the ascending and the descending branches of the Hadley and Walker circulations during both ENSO and non-ENSO periods. The latent heat flux is then computed with a bulk parameterization model. At monthly and 2¿ latitude by 2¿ longitude resolution, the random error of the computed latent heat flux is estimated to approximately 26 W/m2 with the flux variability in the order of 100 W/m2. In areas covered by surface convergence, the moisture flux is found to be low, with the temporal variability due mostly to the variability of wind speed. Elsewhere, the variability of sea-air humidity difference plays a more important role.

During the early phase of the 1982--1983 ENSO, a surface convergence center moves east leading the anomalous equatorial westerlies. At this center, the low wind and high humidity caused negative (low) latent heat flux anomalies despite anomalously high sea surface temperatures. Latent heat flux is found to play an important role in the seasonal cooling of the upper ocean except in areas covered by major surface convergence zones where the variability of insolation is expected to be large and in areas of ocean upwelling where ocean dynamics perturb the upper ocean heat balance. The latent heat flux from the general circulation model of the European Center of Medium Range Weather Forecast is found to be inadequate in capturing the temporal and spatial variations computed from the satellite data. ¿ American Geophysical Union 1988