New evidence for the stratospheric dehydration mechanism in the equatorial Pacific

Water vapor profile measurements obtained in the western and central Pacific during the Central Equatorial Pacific Experiment (CEPEX) show a strong connection between the water vapor content near the tropopause and areas of deep convection. We show that air ascending within deep convective towers can be dried to mixing ratios below 1 part per million by volume (ppmv), which is much lower than the average mixing ratio observed in the stratosphere. A sharp increase of water vapor mixing ratio above the tropopause is an indication of the evaporation of ice particles at the top of deep convective cells. A mixed layer of up to around 1 km thickness above the tropopause in the regions of deep convection is indicated by the vertical profiles of ozone, water vapor, and potential temperature. Furthermore, a local maximum was observed at 20 km, which is an indication for the seasonal cycle of the tropopause temperature.