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| Titel |
Troposphere-stratosphere exchange - constraints from water vapour |
| VerfasserIn |
Y. Liu, S. Fueglistaler, P. H. Haynes |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024699
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| Zusammenfassung |
| Troposphere-to-stratosphere transport involves both cross-isentropic transport across the
tropical tropopause to the stratospheric ‘overworld’ and quasi-horizontal transport
into the lowermost stratosphere. The distribution of stratospheric water vapour is
sensitively dependent on the detailed temperature history of air parcels entering the
stratosphere, which can be used to constrain troposphere-stratosphere exchange
pathways. We carry out trajectory calculations for the years 2001 and 2005-2008
with winds and diabatic heating rates from the ECMWF 40-year reanalysis project
(ERA-40) and the new interim reanalysis project (ERA-Interim). Trajectories are
either kinematic, where the vertical velocity is calculated from mass continuity, or
diabatic, where diabatic heating rates are used to drive cross-isentropic motion. Water
vapour is estimated using a simple dehydration model, and results are compared with
measurements from HALOE and the Microwave Limb Sounder (MLS) on board the AURA
satellite.
In general diabatic trajectories yield spatial and temporal variations in water vapour that
are in better agreement with observations, but for the ERA-Interim dataset the differences
between kinematic and diabatic trajectories are small. Diabatic trajectories, which
give the best estimate in seasonal variation of water vapour, show a consistent dry
bias for the stratospheric overworld of 0.5 ppmv compared to previously published
ERA-40 trajectory results and observations. The results suggest that trajectories
calculated using ERA-40 winds show excessive vertical dispersion which overestimates
troposphere-to-stratosphere exchange, an effect also seen in the lowermost stratosphere. The
new results suggest that moistening processes in addition to the instantaneous dehydration to
large-scale saturation mixing ratio could contribute up to 0.5 ppmv to stratospheric H2O. |
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