Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data

The freshwater flux and the related energy fluxes at the air sea interface are among the most challenging parameters to be derived from satellite measurements. The knowledge of turbulent fluxes between the ocean and the atmosphere along with the radiative fluxes are of major importance to increase the understanding of the climate system. High accuracy fields of these fluxes may be used for direct forcing of ocean circulation models or for evaluating results of coupled climate models exhibiting uncertainties at the air-sea interface.

Conventional estimates of the global freshwater flux between the ocean and the atmosphere are of limited quality due to inadequate spatial and temporal sampling with the exception of the North Atlantic. Additionally, the parameters that determine the freshwater flux are very difficult to measure by buoys or ships. Satellite measurements therefore provide the possibility to circumvent some of these difficulties. In the last two decades many efforts have been spent in developing methods to derive geophysical parameters like the water vapour content, radiative fluxes, etc. from geostationary and polar orbiting satellites. Retrievals developed for radiometers on polar orbiting satellites e.g. the AVHRR (Advanced Very High Resolution Radiometer) on the NOAA series or the SSM/I (Special Sensor Microwave/Imager) on board the DMSP satellites are distinguished by accuracies that are at least competitive or even better than to those of the in situ measurements.

This section describes the used satellite retrievals, including their parameterisation, and empirical assumptions necessary for the determination of the freshwater flux at the air-sea interface, that is defined as the difference between the sink evaporation and the source precipitation.

The evaporation at the sea surface is parameterised using the bulk approach. The wind speed u, the saturation specific humidity at the sea surface q_s, and the atmospheric specific humidity q_l are determined from satellite measurements.