Water vapor transport and dehydration above convective outflow during Asian monsoon

We investigate the respective roles of large-scale transport and convection in determining the water vapor maximum at 100 hPa in the Asian monsoon region. The study uses backward trajectories with ECMWF ERA-Interim heating rates. It includes simple microphysics with supersaturation and takes into account convective sources based on CLAUS data with a simple parameterization of overshoots. A good agreement between reconstructed water vapor and observations is obtained over Asia. It is found that parcels belonging to the water vapor maximum have been first lifted by convection over the Bay of Bengal and the Sea of China and then transported through the tropical tropopause layer (TTL) via the monsoon anticyclonic circulation towards North-West India, where they are eventually dehydrated, avoiding the coldest temperatures of the TTL. Convective moistening accounts for about 0.3 ppmv in the Asian monsoon region and overshoots do not have a significant impact on the water vapor budget. Copright 2008 by the American Geophysical Union.