The tropical tropopause layer (TTL) represent a crucial region in the climate system as it regulates much of the tracer flux into the stratosphere. Most importantly, the stratospheric water vapor content is determined by temperatures in the TTL through dehydration by freeze-drying of air as it ascents through the tropical tropopause. On the other hand, deep convection can loft ice into the TTL, which can cause hydration of stratospheric air. Convectively generated gravity waves produce temperature variations in the TTL, which can significantly alter the coldest points encountered by air parcels and therefore enhance dehydration. These gravity waves might a lso break near the tropopause and drive vertical mixing of constituents between the TTL and lower stratosphere.

Here, an analysis of gravity wave activity in the TTL and lower stratosphere is presented. We present evidence that gravity wave-driven vertical mixing plays an important role for tracer transport just above the tropical tropopause. We also discuss modulation of gravity wave activity by the Madden-Julian Oscillation (MJO). The MJO is the dominant source of intra-seasonal variability in the tropics related to eastward propagating organized convection. Since convection represents the dominant source for gravity wave activity in the tropics the MJO is expected to modulate gravity wave activity in the TTL and lower stratosphere. Preliminary analysis using high-resolution radiosonde data collected during the DYNAMO field campaign shows, however, that lower stratospheric gravity wave activity is not significantly modulated by the MJO.

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*email: thomas.birner@colostate.edu
*Preference: Invited