Response of the intertropical convergence zone to zonally-asymmetric surface forcings

Recent studies have emphasized the importance of energy fluxes and energy input into the tropical atmosphere in determining the response of the intertropical convergence zone (ITCZ) to an imposed forcing. This energetic framework predicts no ITCZ shift in response to an energetic perturbation with zero zonal-mean component but large zonal asymmetries. Here we show the ITCZ exhibits a significant southward shift in response to a zonally-asymmetric forcing from ocean heat transport in a slab-ocean aquaplanet model. The ITCZ response results from the rectification of the forcing by cloud and water vapor radiative feedbacks in the radiator fin region, which leads to a zonal-mean sea-surface temperature cooling and strong anomalous Hadley circulation. However, in the absence of radiative feedbacks, the circulation response is dominated by the furnace regime, involving latent heat release and stationary Rossby wave transport. The energetic framework breaks down in the furnace regime because the dynamics are dominated by stationary eddy transport. As a result, Hadley circulation energy and moisture transport are correlated instead of anti-correlated. Overall our results show the rectification of zonally-asymmetric forcings plays an important role in zonal-mean ITCZ dynamics and highlight the importance of assessing both energy and momentum budgets when interpreting ITCZ shifts.