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Volume 15, issue 6
Atmos. Chem. Phys., 15, 3517–3526, 2015
https://doi.org/10.5194/acp-15-3517-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 15, 3517–3526, 2015
https://doi.org/10.5194/acp-15-3517-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 31 Mar 2015

Research article | 31 Mar 2015

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

T. Wang1,2, A. E. Dessler1, M. R. Schoeberl3, W. J. Randel4, and J.-E. Kim5 T. Wang et al.
  • 1Texas A&M University, College Station, Texas, USA
  • 2NASA Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California, USA
  • 3Science and Technology Corporation, Columbia, Maryland, USA
  • 4National Center for Atmospheric Research, Boulder, Colorado, USA
  • 5University of Colorado, Boulder, Colorado, USA

Abstract. Lagrangian trajectories driven by reanalysis meteorological fields are frequently used to study water vapor (H2O) in the stratosphere, in which the tropical cold-point temperatures regulate the amount of H2O entering the stratosphere. Therefore, the accuracy of temperatures in the tropical tropopause layer (TTL) is of great importance for understanding stratospheric H2O abundances. Currently, most reanalyses, such as the NASA MERRA (Modern Era Retrospective – analysis for Research and Applications), only provide temperatures with ~ 1.2 km vertical resolution in the TTL, which has been argued to miss finer vertical structure in the tropopause and therefore introduce uncertainties in our understanding of stratospheric H2O. In this paper, we quantify this uncertainty by comparing the Lagrangian trajectory prediction of H2O using MERRA temperatures on standard model levels (traj.MER-T) to those using GPS temperatures at finer vertical resolution (traj.GPS-T), and those using adjusted MERRA temperatures with finer vertical structures induced by waves (traj.MER-Twave). It turns out that by using temperatures with finer vertical structure in the tropopause, the trajectory model more realistically simulates the dehydration of air entering the stratosphere. But the effect on H2O abundances is relatively minor: compared with traj.MER-T, traj.GPS-T tends to dry air by ~ 0.1 ppmv, while traj.MER-Twave tends to dry air by 0.2–0.3 ppmv. Despite these differences in absolute values of predicted H2O and vertical dehydration patterns, there is virtually no difference in the interannual variability in different runs. Overall, we find that a tropopause temperature with finer vertical structure has limited impact on predicted stratospheric H2O.

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We investigated the impacts of vertical temperature structures on trajectory simulations of stratospheric dehydration and water vapor by using 1) MERRA temperatures on model levels; 2) GPS temperatures at finer vertical resolutions; and 3) adjusted MERRA temperatures with finer vertical structures induced by waves. We show that despite the fact that temperatures at finer vertical structures tend to dry air by 0.1-0.3ppmv, the interannual variability in different runs is essentially the same.
We investigated the impacts of vertical temperature structures on trajectory simulations of...
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