Estimating Meridional Energy Transports by the Atmospheric and Oceanic General Circulations Using Boundary Fluxes

Abstract

The annual-mean meridional energy transport in the atmosphere?ocean system (total transport) is estimated using 4-yr mean net radiative fluxes at the top of the atmosphere (TOA) calculated from the International Satellite Cloud Climatology Project cloud datasets. In addition, the net atmospheric and surface radiative fluxes are calculated. When supplemented by a climatology of the surface latent and sensible heat fluxes, these radiative fluxes are used to derive the separate atmospheric and oceanic energy transports using a surface and planetary energy-balance method. Most previous results are based on direct calculations of the atmospheric energy transport from in situ measurements of horizontal wind velocity, temperature, and humidity in the atmosphere and on inference of oceanic heat transports as the difference between the atmospheric transports and the total energy transport (the planetary energy-balance method). Total, atmospheric, and oceanic energy transports from this study are in good agreement with more recent results (within mutual uncertainties). A detailed assessment is made of the uncertainties in the atmospheric and ocean energy transports that arise from uncertainties in the TOA and surface energy fluxes: the largest uncertainties are associated with the surface radiative and latent heat fluxes. Since the errors in the present method are from different sources and have different geographic distributions, the results of this study complement previous estimates of the atmospheric and oceanic energy transports. Assessment of error sources also suggests that improvement of this type of result is more likely in the near future than for the other methods. Because the radiative fluxes are calculated from physical quantities, the authors can characterize the mean effects of clouds on the atmospheric and oceanic energy transports: 1) cloud effects on the TOA radiation budget reduce hemispheric differences introduced by hemispheric differences of surface properties, 2) the cloud effects on the atmospheric and surface radiation budgets induce hemispheric differences in the heating/cooling of the atmosphere and ocean that require cross-equatorial transports in opposite directions by the atmosphere and ocean, and 3) all other factors held constant, clouds tend to reduce oceanic energy transports and increase atmospheric energy transports.