Dependence of tropical precipitation on changes in cross-equatorial atmosphere and ocean heat transport in global warming simulations

Abstract

The Intertropical Convergence Zone (ITCZ) is an area of convection encircling the earth near the equator where the northern and southern hemisphere (SH) Hadley cells converge. If a forcing (e.g. aerosol emissions decline) results in a greater net influx of heat into one hemisphere the Hadley cells will shift across the equator to transport heat from the warmer to the cooler hemisphere resulting in a shift of the annual mean location of the ITCZ. Shifts in the annual mean location of the ITCZ can significantly impact the nearly 3 billion who live in the tropics and depend on the ITCZ as a source of freshwater. Recent studies have shown the extent to which the Hadley cells will shift is dependent not only on the magnitude of the forcing but also the cross-equatorial ocean heat transport. In this study, we use Coupled Model Intercomparison (CMIP) output to determine the thermal forcings that result in hemispheric heating asymmetries and induce an ITCZ shift in the 21st century. Using a fully coupled model we also determine the atmosphere will transport most of the total cross-equatorial heat transport if the thermal forcing is applied in the northern hemisphere.