Estimating ocean-atmosphere exchanges from Space

The ocean interacts with the atmosphere in a broad spectrum of scales. Sufficient coverage may only be achieved from the vantage point of space. However, spacebased sensors measured only radiance and backscatter. Gallant efforts have been made in the past two decades to retrieve the exchanges of momentum, heat, and water from spacebased observations with various degree of success. An overview of these efforts will be presented.

Momentum flux is resulted from wind shear. The scatterometer is the proven mean of estimating ocean surface wind vectors, but the capability of polarimetric radiometer is measuring both wind direction and speed is being tested. Evaporation and latent heat it carries are pivotal in estimating both the heat and water exchanges; the method of its estimation from radiometers will be reviewed. Evaporation combines with precipitation will give the water flux. Precipitation has been retrieved from infrared and microwave radiometers, as well as from radar. The water flux can also be estimated from the divergence of the integrated moisture transport in the atmosphere. Heat flux can be divided into four components; sensible heat resulted from thermal gradient, LH carried by evaporation, shortwave radiation (SR) from the sun and longwave radiation from the atmosphere and the ocean. SR and LH are the larger variable components over most of the tropical and temperate oceans and the estimation for satellite observations have been well studied.

There is no direct measurement of all the flux components except a few locations and controlled experiment sites. The validation of these satellite-derived fluxes through applications will be discussed.