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Lagrangian trajectories driven by reanalysis meteorological fields arefrequently used to study water vapor (H2O) in the stratosphere, in whichthe tropical cold-point temperatures regulate the amount of H2O enteringthe stratosphere. Therefore, the accuracy of temperatures in the tropicaltropopause layer (TTL) is of great importance for understanding stratosphericH2O abundances. Currently, most reanalyses, such as the NASA MERRA(Modern Era Retrospective – analysis for Research and Applications), onlyprovide temperatures with ~ 1.2 km vertical resolution in the TTL,which has been argued to miss finer vertical structure in the tropopause andtherefore introduce uncertainties in our understanding of stratosphericH2O. In this paper, we quantify this uncertainty by comparing theLagrangian trajectory prediction of H2O using MERRA temperatures onstandard model levels (traj.MER-T) to those using GPS temperaturesat finer vertical resolution (traj.GPS-T), and those using adjustedMERRA temperatures with finer vertical structures induced by waves(traj.MER-Twave). It turns out that by using temperatures with finervertical structure in the tropopause, the trajectory model more realisticallysimulates the dehydration of air entering the stratosphere. But the effect onH2O abundances is relatively minor: compared with traj.MER-T,traj.GPS-T tends to dry air by ~ 0.1 ppmv, whiletraj.MER-Twave tends to dry air by 0.2–0.3 ppmv. Despite thesedifferences in absolute values of predicted H2O and vertical dehydrationpatterns, there is virtually no difference in the interannual variability indifferent runs. Overall, we find that a tropopause temperature with finervertical structure has limited impact on predicted stratospheric H2O

The impact of temperature vertical structure on trajectory modeling of stratospheric water vapor