Seasonal intertropical convergence zone shift: does energetic theory still work

Abstract:

Annual and zonal mean intertropical convergence zone (ITCZ) position was found to have a relationship with interhemispheric energy transport. The radiative imbalance at the top of the atmosphere (TOA) transported across the equator to the cooler hemisphere explains the ITCZ position and its shift. Using idealized model simulations with a “slab” ocean, researchers found that an increase in the interhemispheric TOA radiation contrast causes an increase in cross-equatorial energy flux by the Hadley circulation and a shift of the ITCZ towards the warmer hemisphere. The theory that relates cross-equatorial energy flux and ITCZ position is called energetic theory.

In our study, we want to examine if this theory can be expanded to a seasonal and regional scale. We analyze Tropical rain belts with an Annual cycle and a Continent-Model Intercomparison Project (TRACMIP), which uses idealized models thermodynamically coupled to a slab ocean. TRACMIP has idealized tropical continent setups with both present-day and quadruple CO2 (4xCO2) concentration experiments which can help us understand ITCZ shift under a warming scenario. Our current findings suggest that energetic theory cannot explain the ITCZ position change between 4xCO2 and present-day experiments, while mass transport by the Hadley circulation agrees with the ITCZ shift at a seasonal scale.

In the future, we will try to understand why energetic theory does not predict the ITCZ shift as well as Hadley cell change at a seasonal scale. We will examine the response of other mechanisms including but not limited to monsoon circulations, transient and stationary eddies to 4xCO2 scenario. We aim to have a deeper understanding of the energetic theory to give insight to real-world tropical rainfall change under a warming scenario.