Toward Consistent Diagnostics of the Coupled Atmosphere and Ocean Energy Budgets

Abstract

The widely used diagnostic vertically integrated total energy budget equations of atmosphere and ocean contain inconsistencies that should no longer be disregarded. The neglect of enthalpy fluxes associated with precipitation and evaporation leads to a spurious dependence on reference temperature. This seemingly small inconsistency is amplified because enthalpy of water vapor implicitly included in lateral atmospheric energy transports usually is computed on the Kelvin scale, leading to inconsistencies that, although zero when globally averaged, attain values on the order of 20 W m−2 in the tropics. A more consistent energy budget framework is presented, which is independent of reference temperature and which takes full account of enthalpy fluxes associated with mass transfer through the surface. The latter include effects of snowfall and additional nonlatent contributions, which have a net cooling effect on the earth’s surface (−1.3 W m−2). In addition to these diagnostic issues, comparatively small inconsistencies in the energetic formulations of current weather and climate models are highlighted. Using the energy budget formulation presented here, instead of that commonly used, yields enhanced self-consistency of diagnosed atmospheric energy budgets and substantially improved spatial agreement between fields of net surface energy flux inferred from the divergence of lateral atmospheric energy transports in conjunction with satellite-based radiative fluxes and independent surface flux products. Results imply that previous estimates of radiative plus turbulent surface fluxes over the ocean, balancing the observed ocean warming, are biased low by ~1.3 W m−2. Moreover, previous studies seriously underestimated cross-equatorial atmospheric and oceanic energy transports. Overall, the presented framework allows for unambiguous coupled energy budget diagnostics and yields more reliable benchmark values for validation purposes.