Feedback of Atmosphere–Ocean Coupling on Shifts of the Intertropical Convergence Zone

It is well known that the intertropical convergence zone (ITCZ) shifts in response to remote perturbations to the atmospheric energy balance, with shifts roughly in proportion to changes in the cross-equatorial atmospheric energy flux. However, atmospheric and oceanic energy fluxes in low latitudes are mechanically coupled, and the oceanic energy flux dominates the atmospheric energy flux. Here a quantitative relation is derived that shows how coupling of atmospheric and oceanic energy fluxes in low latitudes damps the response of the energy flux equator (EFE) and ITCZ to perturbations. To first order, the response of the EFE and ITCZ in the coupled atmosphere-ocean system to perturbations is muted by a factor γ =1 + O₀/NEI₀, where O₀ is the ocean energy uptake and NEI₀ is the net energy input into the atmosphere at the equator. In the current climate in the zonal and annual mean, this factor is about γ ≈ 3.