Atmospheric heating in the tropics: Past, present and future

Atmospheric heating in the tropics is provides the fuel that drives tropical weather and climate variability on temporal scales ranging from the life cycle of tropical disturbances to the modulation of long-term climate variability, being central to both and natural and anthropogenic climate change. Tropical atmospheric heating also modulates global teleconnections. In this study we evaluate the evolution of atmospheric heating in the tropics in past, present and future climates. Evidence is found of an interannual atmospheric heating contrast over land and ocean and with a marked anti-correlation on interannual time scales. Results suggest that heating variability over the Indian Ocean plays a major role in modulating this inverse relationship. With the increase in SST during the 20th century, the area of the traditionally defined oceanic warm pool corresponding to the region occupied by sea surface temperatures above a pre-defined threshold (e.g. 28ºC) has increased considerably. However, the area corresponding to the region of atmospheric heating in the tropics, here termed the dynamic warm pool (DWP), has remained constant. In other words, in a warming climate the convective area has not expanded with the area of SST>28ºC. Nevertheless, the magnitude of the column integrated heating in the tropics increases substantially with SST. In addition we use model simulations from the Coupled Model Intercomparison Project (CMIP) and the Paleoclimate Modelling Intercomparison Project (PMIP) to explore the behavior of atmospheric heating and the area of the DWP during the 21st century, and in past climates, respectively. In past climates we focus on the mid-Holocene (6,000 yr BP) and the last glacial maximum (21,000 yr BP). During the last glacial maximum, SST's in the tropics were about 3 to 4°C cooler than today. In contrast, the mid-holocene was a considerably warmer periods, especially during the northern hemisphere summer. We pose hypotheses to explain the constancy of the DWP, the changes in integrated heating and the anti-correlation of heating between land and ocean.