A comparison of ATTREX H2O observations in the TTL with values derived from reanalysis-based back trajectories

Abstract:

Despite very low mixing ratios relative to the troposphere, water vapor in the lower stratosphere (LS) plays a significant role in Earth’s radiative balance and climate system, and is an important constituent in stratospheric chemistry. The low H₂O content of air entering the LS is established to first order by dehydration processes controlled by the cold temperatures of the tropical tropopause layer (TTL), especially over the western Pacific. Global climate models rely on parameterizations in order to simulate TTL dehydration processes and calculate the amount of H₂O transported into the stratosphere. Here we present an analysis of in situ water vapor measurements in the western Pacific TTL from the NASA ATTREX campaign and compare them to reanalysis-based back trajectory calculations of LS H₂O in order to investigate the efficiency of TTL dehydration processes and provide constraints on the representation of TTL dehydration in reanalyses and global models.