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- Title
Sensitivity of stratospheric water vapour to variability in tropical tropopause temperatures and large-scale transport.
- Authors
Smith, Jacob W.; Haynes, Peter H.; Maycock, Amanda C.; Butchart, Neal; Bushell, Andrew C.
- Abstract
Concentrations of water vapour entering the tropical lower stratosphere are primarily determined by conditions that air parcels encounter as they are transported through the tropical tropopause layer (TTL). Here we quantify the relative roles of variations in TTL temperatures and transport in determining seasonal and interannual variations of stratospheric water vapour. Following previous studies, we use trajectory calculations with the water vapour concentration set by the Lagrangian Dry Point along trajectories. To isolate the roles of transport and temperatures, the Lagrangian Dry Point calculations are modified by time-shifting temperatures relative to transport, and vice versa, with the shift made by years to investigate interannual variations and by months to investigate seasonal variations. Both ERA-Interim reanalysis data for the 1999-2009 period and data generated by a chemistry-climate model (UM-UKCA) are investigated. Variations in temperatures, rather than transport, dominate interannual variability, typically explaining more than 70% of variability, including individual events such as the 2000 stratospheric water vapour drop. Similarly seasonal variation of temperatures, rather than transport, is shown to be the dominant driver of the annual cycle in lower stratospheric water vapour concentrations in both model and reanalysis, but it is also shown that seasonal variation of transport plays an important role in reducing the seasonal cycle maximum (reducing the annual range by about 30%).
- Subjects
WATER vapor; SEASONAL temperature variations; TROPOPAUSE; VAPORS; LAGRANGIAN points
- Publication
Atmospheric Chemistry & Physics Discussions, 2020, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2020-934