Impact of monsoon circulations on the upper troposphere and lower stratosphere

Observations from in situ aircraft and output from a global chemical transport model are used to better understand the impact of Northern Hemisphere summer monsoon circulations on stratosphere-troposphere exchange. A long-term model climatology resembles the satellite climatology of water vapor and ozone in the monsoon regions. A simulation with observed winds is able to reproduce individual transport events observed from aircraft, and these events are used to infer that large-scale motions and monsoon circulations can explain the global correlations of ozone and water vapor around the tropopause. A detailed analysis of model fluxes of water vapor and ozone indicates that the Asian monsoon circulation may contribute 75% of the total net upward water vapor flux in the tropics at tropopause levels from July to September. Some of this air may enter the tropical stratosphere and bypass the tropical tropopause altogether.