Uncertainties in global ocean surface heat flux climatologies derived from ship observations

Abstract

A methodology to define uncertainties associated with ocean surface heat flux calculations has been developed and applied to a revised version of the Oberhuber global climatology, which utilizes a summary of the COADS surface observations. Systematic and random uncertainties in the net oceanic heat flux and each of its four components at individual grid points and for zonal averages have been estimated for each calendar month and the annual mean. The most important uncertainties of the 2{degree} x 2{degree} 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{sup {minus}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{sup {minus}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{sup {minus}2} nearly everywhere south of 40{degree}N, and in excess of 30 W m{sup {minus}2} over broad areas of the subtropics, even those with large numbers of observations. Resulting zonal mean latent heat flux uncertainties are largest ({approximately}30 W m{sup {minus}2}) in the middle latitudes and subtropics and smallest ({approximately}10--25 W m{sup {minus}2}) near the equator and over the northernmost regions.