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| Titel |
Stratospheric transport and age-of-air from CTM simulations with ERA-Interim: agreement with observational trends |
| VerfasserIn |
B. M. Monge-Sanz, M. P. Chipperfield, D. P. Dee, A. J. Simmons, S. M. Uppala, G. P. Stiller |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069640
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| Zusammenfassung |
| Stratospheric simulations carried out with a chemistry transport model (CTM) are used to
evaluate the stratospheric Brewer-Dobson circulation and mixing processes in different
datasets produced by the European Centre for Medium-Range Weather Forecasts (ECMWF).
A comparison between ERA-40 and ERA-Interim shows that the recent ECMWF reanalysis
greatly overcomes problems detected in the past for ERA-40. CTM simulations with
ERA-Interim provide improved age-of-air (AoA) distributions, in very good agreement with
observations in the lower stratosphere.
Our AoA results have been validated against standard observation-based datasets (Ray et
al., 1999; Andrews et al., 2001) and also against the new observational AoA dataset
derived from recent MIPAS SF6 measurements (Stiller et al., 2011). Our model
results with ERA-Interim fields disagree with the decrease tendency in age-of-air
widespread in most models (e.g. WMO, 2011), but are in good agreement with recent
age-of-air studies based on observations (Engel et al., 2009; Waugh, 2009; Stiller et al.,
2011).
We have also performed Lagrangian trajectory runs in the lower stratosphere. The
quantification of tropical dispersion from our Lagrangian calculations shows that the
constraint of the vertical and horizontal mixing has been very significantly improved
in the new ECMWF reanalysis dataset. Tape recorder simulations also confirm
this.
Causes of the improvements achieved by the new reanalysis are explored, pointing
towards the roles that the assimilation technique and the analysis read-in frequency play in
the successful description of stratospheric transport in the CTM. Some of the problems
attributed in the past to data assimilation, such as the excess of vertical mixing in the lower
stratosphere, are here shown to be also caused by too low read-in frequencies in the CTM
simulations. In this study we also show that the implementation of correction techniques,
such as the use of forecasts instead of analyses, have a smaller effect in CTM simulations
with ERA-Interim than with ERA-40.
References:
Andrews AE, et al. 2001. J. Geophys. Res. 106: 32295–32314.
Engel A, et al. 2009. Nat. Geosci. 2: 28–31.
Ray EA et al. 1999. J. Geophys. Res. 104: 26565–26580.
Stiller GP. 2011. Atmos. Chem. Phys. Discuss.11: 28013–28059.
Waugh D. 2009. Nat. Geosci. 2: 14–16.
WMO. 2011. Global Ozone Research and Monitoring Project -Report No. 52. |
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