Changes in Tropical Regional Circulation Under Global Warming: The Role of Vertical Structure of Convection in Current Climate

The dynamic contribution associated with the change in atmospheric vertical motion shows large spatial variation and plays an important role in affecting regional precipitation in global warming simulations. However, changes in atmospheric vertical motion can be either strengthened or weakened, even within convective areas with positive rainfall anomalies. To understand the diverse responses of changes in tropical circulation in a warmer climate and the associated mechanisms, we investigated the vertical structure of convection and atmospheric stability from 32 coupled global climate models in CMIP3 and CMIP5. The study regions are convection zones with positive precipitation anomalies, where both enhanced and reduced ascending motions are found. Under global warming, an upward-shift structure of ascending motion is observed in the entire domain, implying a deepening of convection and a more stable atmosphere, which leads to a weakening of tropical circulation. Regionally, areas with enhanced (weakened) ascending motion are associated with a more (less) import of moist static energy by a climatologically bottom-heavy (top-heavy) structure of vertical velocity. Therefore, different climatological vertical profile tends to induce the different change in atmospheric stability: the bottom-heavy (top-heavy) structure brings a more (less) unstable condition, and is favorable (unfavorable) to the strengthening of convective circulation. The bottom-heavy structure is associated with shallow convection, while the top-heavy structure is usually related to deep convection. In other words, shallow convection tends to strengthen tropical circulation and enhances upward motion in future warmer climate. This study provides a linkage for projecting and understanding future circulation change from current climate.