Weakening of the tropical tropopause layer cold trap with global warming

Abstract. Lagrangian trajectories have previously been used to reconstruct water vapor variability in the lower stratosphere, where sensitivity of surface radiation changes concentration is strongest, by obtaining temperature histories air parcels that ascend from troposphere stratosphere through tropical tropopause layer (TTL). Models and theory predict an acceleration Brewer–Dobson circulation (BDC) deceleration Walker with warming, both these will drive future transport across TTL. Here, we examine response TTL during boreal winter idealized BDC comparing computed ERA5 data those calculated using same but altered vertical zonal wind velocities. We find lower-stratospheric mixing ratios trajectories' cold point temperatures can increase about 1.6 ppmv (about 50 %) when only winds are slowed, while a negligible impact on concentrations. This change follows decrease sampling field trajectories, which weakens “cold trap” mechanism dehydration as evolves. As decrease, fraction passes trap ascending coldest average experienced increase. Future be applied offset histories, including enhanced warming due El Niño-like has secondary dehydrated trap. Some resultant moistening may negated decreased rate following point, allow more ice gravitationally settle before sublimating outside result presents for stratospheric feedback exist without temperatures.