Tropical circulation and associated precipitation responses under idealized global warming simulations

Abstract. The Inter-Tropical Convergence Zone (ITCZ) is a major precipitation feature in the global equatorial regions and a crucial part of the tropical atmospheric circulation. Due to its effects on the Hadley circulation, changes in the position and characteristics of the ITCZ can have a cascading impact not only in tropical regions that receive abundant precipitation throughout the year but also in adjacent sub-tropical regions that receive less rainfall, mostly in certain seasons. Aiming for a better understanding of tropical and sub-tropical precipitation dynamics, here we study the changes in the ITCZ position and characteristics, including the edges and strength, across various longitudinal bands for 2 °C and 4 °C Global Warming Levels (GWLs) above the pre-industrial conditions. Our analysis is based on idealized simulations from the Tipping Points Inter-comparison Project (TIPMIP). Shifts in the characteristics of the ITCZ are contrasted with the changes in the tropical and sub-tropical precipitation from these idealized experiments. Additionally, the variations in the regional zonal mean of the pressure velocity, as well as the global zonal mean of the mass streamfunction and pressure velocity, are assessed for both GWLs and compared with the modifications in the ITCZ location and associated precipitation. Our results show that the global zonal mean ITCZ will contract with a higher global mean temperature, with a general displacement toward the winter hemisphere. In the various regions, the ITCZ response to increasing global temperatures generally varies, but overall, weaker updrafts are projected. The precipitation intensity of the ITCZ band becomes stronger, despite the weakening of the Hadley cell circulation and its ascending and descending branches, with decreased precipitation projected in the descending branch over the sub-tropics.