Spatiotemporal Variability of the Tropical Dynamical Warm Pool

The convective activity in the tropic plays a crucial role in the global climate and in its response to changes in the magnitude of the external forcing factors. Twentieth-century observations show that during the last 60 years the sea-surface temperature (SST) of the tropical ocean has increased by 0.7°C and the area of SST>26.5 and 28°C (oceanic warm pool -OWP -) traditionally associated with convective activity, by 15 and 50% respectively. Analysis of 20th-century observations and CMIP3/CMIP5 models show that the tropical OWP has increased in area by nearly 70% since 1910 and is projected to double during the 21st century in association with greenhouse warming in a moderate CO2 forcing scenario. However, during the same period the dynamical warm pool (DWP), defined as the area of positive atmospheric heating, has remained constant. The threshold SST (TH), which shows the region of net heating and cooling, has increased from 26.6°C in the 50s to 27.1°C in the last decade and it is projected to increase to 28.5°C by 2100 in the CMIP3/CMIP5 simulations. The DWP area is projected to remain constant during the 21st century. The area of the DWP remains constant while SSTs increase across the tropics as a result of a balance between increases in convective heating within the DWP and radiative cooling outside the DWP. Although the area of the DWP remains constant, the total tropical atmospheric heating has increased by around 10% from 1950 to 2000, and it is projected to further increase another 10% by 2100. The increase in heating suggests an enhancement of the global hydrological cycle and potentially of the atmospheric circulation, with growth in convective heating within the DWP, and an increase of subsiding air and stability outside the convective warm pool and vertical shear in the DWP boundaries. Finally, changes in the intensity of the Hadley and Walker cells are assessed from the perspective of the discussed DWP and atmospheric heating changes. The spatial structure of convective warming presents positive and negative regional trend patterns that coincide with observed global precipitation trends.