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The Asian monsoon region is the most prominent moisture center of water vaporin the lower stratosphere (LS) during boreal summer. Previous studies havesuggested that the transport of water vapor to the Asian monsoon LS iscontrolled by dehydration temperatures and convection mainly over the Bay ofBengal and Southeast Asia. However, there is a clear geographic variation ofconvection associated with the seasonal and intra-seasonal variations of theAsian monsoon circulation, and the relative influence of such a geographicvariation of convection vs. the variation of local dehydration temperatureson water vapor transport is still not clear. Using satellite observationsfrom the Aura Microwave Limb Sounder (MLS) and a domain-filling forwardtrajectory model, we show that almost half of the seasonal water vaporincrease in the Asian monsoon LS are attributable to geographic variations ofconvection and resultant variations of the dehydration center, of which theinfluence is comparable to the influence of the local dehydration temperatureincrease. In particular, dehydration temperatures are coldest over thesoutheast and warmest over the northwest Asian monsoon region. Although theconvective center is located over Southeast Asia, an anomalous increase ofconvection over the northwest Asia monsoon region increases localdiabatic heating in the tropopause layer and air masses entering the LS aredehydrated at relatively warmer temperatures. Due to warmer dehydrationtemperatures, anomalously moist air enters the LS and moves eastward alongthe northern flank of the monsoon anticyclonic flow, leading to wet anomaliesin the LS over the Asian monsoon region. Likewise, when convection increasesover the Southeast Asia monsoon region, dry anomalies appear in the LS.On a seasonal scale, this feature is associated with the monsoon circulation,convection and diabatic heating marching towards the northwest Asiamonsoon region from June to August. The march of convection leads to anincreasing fraction of the air mass to be dehydrated at warmer temperaturesover the northwest Asia monsoon region. Work presented here confirms thedominant role of temperatures on water vapor variations and emphasizes thatfurther studies should take geographic variations of the dehydration centerinto consideration when studying water vapor variations in the LS as it islinked to changes of convection and large-scale circulation patterns

Impact of geographic variations of the convective and dehydration center on stratospheric water vapor over the Asian monsoon region