Uncertainties in estimates of surface heat fluxes derived from marine reports over the tropical and subtropical oceans

Abstract

Estimates are made of the uncertainties in calculations of the heat fluxes at the surface of the tropical and subtropical oceans based upon the bulk formulae and archived marine weather reports. Major contributions are identified not only in the basic observations of such variables as temperature and wind but also in uncertainties in parameters in the bulk formulae themselves. All identified factors are defined as either random or systematic. The potential effects of archiving and sampling errors are also explored. The total uncertainties for individual observations of the net solar and infrared irradiances and the latent and sensible heat fluxes are about 80, 10, 83 and 12 W m^-2, respectively. Because uncertainties associated with random errors decrease when many observations are averaged, the uncertainties in the fluxes decrease substantially when fifty or more observations are averaged together. However, since all of the surface fluxes have some systematic uncertainties associated with them, sizeable uncertainties remain, especially in the latent heat flux, even if an unlimited number of observations is available for calculating the means. Representative maps of uncertainties in 20-year monthly means of the component fluxes over the tropical Pacific show large uncertainties in the equatorial and southeastern oceans. Elsewhere, the net solar and infrared irradiance and sensible heat flux have uncertainties of 10 W m^-2 or less. Unfortunately, the uncertainties in the latent heat flux exceed 30 W m^-2 everywhere, because of the large systematic component. Total uncertainties in the net heating of the ocean surface are relatively large over the entire tropical Pacific with the smallest relative values in the eastern tropical region.