Theory, observations, and models indicate that the zonally and temporally averaged position of the intertropical convergence zone (ITCZ) is primarily set by northern vs southern hemisphere heating differences, which drive a net cross-Equator atmospheric energy transport (AET). It has been shown with both simple and global models that ITCZ position exhibits secondary sensitivity to the meridional structure of tropical net atmospheric energy input (AEI), which is the residual of column heating by shortwave absorption, column cooling by longwave emission to space, and ocean heat uptake. While AET is driven by integrated heating across each hemisphere, AEI and its meridional structure are sensitive to a variety of local processes, including ocean upwelling and transport, cloud radiative feedbacks, and surface fluxes.

In this study, we explore the effects of the representation of surface fluxes in global models to ITCZ biases in those models. It has been shown that bulk surface flux algorithms used in many climate models overestimate surface fluxes by 10-20% for a given set of bulk inputs (i.e., wind speed, sea surface temperature, and humidity) when compared to direct covariance surface flux measurements. In contrast, the COARE3.0 bulk flux algorithm (Fairall et al. 2003) yields much lower biases. A newly developed surface flux diagnostic allows us to retroactively adjust model fluxes to those that would have been computed with the COARE3.0 algorithm. An “offline” assessment of anticipated changes to the surface fluxes indicates that mean surface fluxes should be substantially reduced in the vicinity of ITCZ biases in models. We next perform an “inline” correction in two climate models by replacing the default bulk flux algorithm with the COARE3.0 bulk flux algorithm. Consistent with the offline correction, the inline correction also reduces ITCZ biases in both models. Finally, we explore the relationship between default and COARE3.0 surface fluxes to atmospheric buoyancy profiles, convection, AEI, and ITCZ position.