The interaction between the dynamics of the atmosphere and the dryness at the surface in the subtropical regions

Principal Investigator: 

Dry regions, where evaporation and evapotranspiration exceeds precipitation in the annual mean, cover about 40% of Earth’s land surface and affect the livelihood of nearly 2 billion people, primarily in developing countries. Drought intensity and frequency may have increased in many dry zones of the subtropics over the past 30 years, and simulations of global warming scenarios for the 21st century provide similar trends. Dryness in the subtropics is expected from the existence of a meridional overturning circulation in the atmosphere, i.e., the Hadley circulation. During the summer season, however, this overturning circulation becomes weak while large zonal asymmetries in precipitation are maintained. Such contrast is especially evident during the late boreal summer season when comparing the extreme dryness over the Sahara desert to the intense monsoonal rains over Southeast Asia. Although a number of mechanisms have been proposed to explain these large contrasts in dryness across the subtropics, their relevance to present day climate or to global climate change scenarios remain uncertain. This project aims at discriminating relevant mechanisms leading to dryness in the subtropics in present day climate conditions, and to quantify their sensitivities to various global climate change scenarios.