Changing links between South Asian summer monsoon circulation and tropospheric land‐sea thermal contrasts under a warming scenario

Abstract

Forced with increased greenhouse gases, the South Asian summer monsoon (SASM) circulation weakens in climate models, which appears inconsistent with the projected increases in near‐surface land‐sea thermal contrasts during the 21st century. Our analysis shows that the SASM intensity positively correlates with the land‐sea thermal contrast in both the lower‐ and upper‐troposphere before year 2000; thereafter a reduced upper‐tropospheric thermal contrast leads to a weakened SASM circulation, despite an increasing lower‐tropospheric thermal contrast. The decrease in the upper‐tropospheric thermal contrast mainly results from enhanced upper‐tropospheric warming over the tropical Indian Ocean due to increased latent heating. The results suggest a crucial role of enhanced tropical convection in the weakening of SASM circulation and a weak influence of lower‐tropospheric thermal contrast on the SASM under global warming. They also imply a less important role of near‐surface processes over the Tibetan Plateau in the long‐term SASM change during the 21st century.