The most important uncertainties of the 2° x 2° grid cell values of each of the heat fluxes are described. Annual mean net shortwave flux random uncertainties associated with errors in estimating cloud cover in the tropics yield total uncertainties which are greater than 25 W m^-2. In the northern latitudes, where the large number of observations substantially reduce the influence of these random errors, the systematic uncertainties in the utilized parameterization are largely responsible for total uncertainties in the shortwave fluxes which usually remain greater than 10 W m^-2. Systematic uncertainties dominate in the zonal means because spatial averaging has led to a further reduction of the random errors. The situation for the annual mean latent heat flux is somewhat different in that even for grid point values the contributions of the systematic uncertainties tend to be larger than those of the random uncertainties at most all latitudes. Latent heat flux uncertainties are greater than 20 W m^-2 nearly everywhere south of 40°N , and in excess of 30 W m^-2 over broad areas of the subtropics, even those with large numbers of observations. Resulting zonal mean latent heat uncertainties are largest (~30 W m^-2) in the middle latitudes and subtropics and smallest (~10-25 W m^-2) near the equator and over the northernmost regions.
Preliminary comparison of zonal average fluxes suggest that most atmospheric general circulation models produce excessively large ocean surface fluxes of net solar heating and evaporative cooling when forced with realistic sea surface temperatures. It is expected that the method introduced here will be refined to produce increasingly reliable estimates of uncertainties in surface flux atlases derived from ship observations. (pdf file)