Lagrangian trajectories driven by reanalysis meteorological fields arefrequently used to study water vapor (HO) in the stratosphere, in whichthe tropical cold-point temperatures regulate the amount of HO enteringthe stratosphere. Therefore, the accuracy of temperatures in the tropicaltropopause layer (TTL) is of great importance for understanding stratosphericHO 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 stratosphericHO. In this paper, we quantify this uncertainty by comparing theLagrangian trajectory prediction of HO using MERRA temperatures onstandard model levels () to those using GPS temperaturesat finer vertical resolution (), and those using adjustedMERRA temperatures with finer vertical structures induced by waves(). 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 onHO abundances is relatively minor: compared with , tends to dry air by ~ 0.1 ppmv, while tends to dry air by 0.2–0.3 ppmv. Despite thesedifferences in absolute values of predicted HO 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 HO.
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