Forecast, observation and modelling of a deep stratospheric intrusion event over Europe

Abstract

A wide range of measurements was carried outin central and southeastern Europe within the frameworkof the EU project STACCATO (Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmo-spheric Transport and Oxidation Capacity) with the princi-ple goal to create a comprehensive data set on stratosphericair intrusions into the troposphere along a rather frequentlyobserved pathway over central Europe from the North Seato the Mediterranean Sea. The measurements were basedon predictions by suitable quasi-operational trajectory cal-culations using ECMWF forecast data. A predicted deepStratosphere to Troposphere Transport (STT) event, encoun-tered during the STACCATO period on 20–21 June 2001,was followed by the measurements network almost from itsinception. Observations provide evidence that the intrusionaffected large parts of central and southeastern Europe. Es-pecially, the ozone lidar observations on 20–21 June 2001 at Garmisch-Partenkirchen, Germany captured the evolutionof two marked tongues of high ozone with the first one de-scending to nearly 2 km, thus providing an excellent data setfor model intercomparisons and validation. In addition, forthe first time to our knowledge concurrent surface measure-ments of the cosmogenic radionuclides10Be and7Be andtheir ratio10Be/7Be are presented together as stratospherictracers in a case study of a stratospheric intrusion. The ozonetracer columns calculated with the FLEXPART model werefound to be in good agreement with water vapour satellite im-ages, capturing the evolution of the observed dry streamersof stratospheric origin. Furthermore, the time-height crosssection of ozone tracer simulated with FLEXPART overGarmisch-Partenkirchen captures many details of the evolu-tion of the two observed high-ozone filaments measured withthe IFU lidar, thus demonstrating the considerable progressin model simulations. Finally, the modelled ozone (oper-ationally available since October 1999) from the ECMWF(European Centre for Medium-Range Weather Forecasts) atmospheric model is shown to be in very good agreementwith the observations during this case study, which providesthe first successful validation of a chemical tracer that is de-rived operationally from a weather forecast model. This sug-gests that coupling chemistry and weather forecast modelsmay significantly improve both weather and chemical fore-casts in the future.