STACCATO: Influence of stratosphere-troposphere exchange in a changing climate on atmospheric transport and oxidation capacity

• Research unit: EU RFP
• Project number: 99.0582-2

Key words (English)

Stratosphere-troposphere exchange; tropopause; dynamical meteorology; trajectories

Alternative project number (English)

EU project number: EVK2-1999-00316

Research programs (English)

EU-programme: 5. Frame Research Programme - 1.4a.2 Global change, climate and biodiversity

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: LMU, München (D)

Abstract (English)

The EU project STACCATO aims at extending our understanding of cross-tropopause exchange in the extra-tropics. It covers (i) observational studies in the Alpine region and in Greece, (ii) a model intercomparison of exchange estimates and (iii) a detailed climatological investigation of cross-tropopause mass fluxes, based upon Lagrangian analyses, for the present climate and for future climate change scenarios.
Our activities contributed to all three topics. (i) As a guidance for the measurement campaigns (lidar observations, ozone soundings, surface observations) trajectories for deep stratospheric intrusions have been calculated in a quasi-operational way (using ECMWF forecast data) and distributed daily to the other partners. (ii) Three case study periods have been selected and quantitative cross-tropopause mass fluxes for the European region have been derived with our technique and delivered to the STACCATO data base. The analysis of the estimates from the various models utilized in the project provided for the first time a detailed intercomparison of 8 different models and techniques. This intercomparison was led by a group in the Nederlands and showed substantial differences in the exchange estimates from the different models. Our fully Lagrangian approach yielded a realistic and very detailed picture of the exchange, and due to the neglection of small-scale turbulence, has a weak tendency to underestimate the exchange. (iii) Our main efforts led to a comprehensive Lagrangian climatology of upward (TST) and downward (STT) cross-tropopause transport in the extratropical Northern Hemisphere for the years 1979-1993 using ECMWF re-analysis data. This considerably extends the previously available climatologies and reveals important novel characteristics of cross-tropopause exchange, in particular the detailed geographical distributions and the seasonal and inter-annual variability of these patterns. Our results show that STT occurs predominantly over the midlatitude storm-track regions, except for summer when the main STT activity is located over southeastern Europe and the Middle East. An additional investigation of tropopause folds, based upon a novel identification technique, revealed that these regions are characterized by frequent tropopause foldings during summer which might explain the intense exchange activity in these areas. In parallel, a special class of tropopause structures (filamentary streamers and cutoff cyclones) have been objectively identified on several isentropic surfaces for the same 15 year time period. Preliminary investigations show a strong link between extratropical exchange events and these mesoscale features.Results from the STACCATO project will be published in a special section in the Journal of Geophysical Research in early 2003; and we contributed to 8 of the submitted papers.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 99.0582-2