Atmos. Chem. Phys. Discuss., 13, 9653-9679, 2013
www.atmos-chem-phys-discuss.net/13/9653/2013/
doi:10.5194/acpd-13-9653-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Modeling upper tropospheric and lower stratospheric water vapor anomalies
M. R. Schoeberl1, A. E. Dessler2, and T. Wang2
1Science and Technology Corporation, Lanham, MD, USA
2Texas A&M University, College Station, TX, USA

Abstract. The domain-filling, forward trajectory calculation model developed by Schoeberl and Dessler (2011) is used to further investigate processes that produce upper tropospheric and lower stratospheric water vapor anomalies. We examine the pathways parcels take from the base of the tropical tropopause layer (TTL) to the lower stratosphere. Most parcels found in the lower stratosphere arise from East Asia, the Tropical West Pacific (TWP) and the Central/South America. The belt of TTL parcel origins is very wide compared to the final dehydration zones near the top of the TTL. This is due to the convergence of rising air as a result of the stronger diabatic heating near the tropopause relative to levels above and below. The observed water vapor anomalies – both wet and dry – correspond to regions where parcels have minimal displacement from their initialization. These minimum displacement regions include the winter TWP and the Asian and American monsoons. To better understand the stratospheric water vapor concentration we introduce the water vapor spectrum and investigate the source of the wettest and driest components of the spectrum. We find that the driest air parcels that originate below the TWP, moving upward to dehydrate in the TWP cold upper troposphere. The wettest air parcels originate at the edges of the TWP as well as the summer American and Asian monsoons. The wet air parcels are important since they skew the mean stratospheric water vapor distribution toward higher values. Both TWP cold temperatures that produce dry parcels as well as extra-TWP processes that control the wet parcels determine stratospheric water vapor.

Citation: Schoeberl, M. R., Dessler, A. E., and Wang, T.: Modeling upper tropospheric and lower stratospheric water vapor anomalies, Atmos. Chem. Phys. Discuss., 13, 9653-9679, doi:10.5194/acpd-13-9653-2013, 2013.
 
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