Intercontinental transport and its influence on the ozone concentrations over central Europe: Three case studies

Abstract

In this paper we report on a detailed analysis of the first clear observation of ozone import from North America in the free troposphere over central Europe in May 1996 and of two more recent cases of transatlantic transport. The analysis is based on calculations with the FLEXTRA trajectory model and the FLEXPART tracer model and data from Measurements of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) flights and North American surface sites. Lidar measurements carried out under conditions of developing anticyclonicity at Garmisch‐Partenkirchen, Germany, consistently yield peak ozone mixing ratios in the middle and upper troposphere between 80 and 110 ppb during the warm season. These layers are traced back to North America by FLEXTRA trajectories. The prevailing transport pathway involves a warm conveyor belt exporting high amounts of ozone, formed during a prefrontal high‐ozone episode, from the central part of the eastern United States to the upper troposphere. The polluted air may enter central Europe above an airstream descending from the stratosphere, thus inverting the normal atmospheric stratification, with stratospheric air at low levels and boundary layer air in the upper troposphere. However, the first two cases studied in this paper show that the export from the eastern United States may arrive over Europe at times prior to the onset of the anticyclonic conditions. Analysis of these cases reveals the complexity of the air export from North America. The ozone maxima occurring during the observational periods are traced back to the planetary boundary layer (PBL) in other source areas in the United States. Some of them are related to entrainments even from source areas beyond North America, either in the stratosphere or in Asia. The third case is quite different in its advection pathway, with almost straight and horizontal advection at 6 to 8 km above sea level starting from the Great Lakes area. A positive correlation between ozone and aerosol in that layer verifies the presence of PBL air. However, the very high ozone mixing ratio (up to 130 ppb) and an anticorrelation of ozone and humidity suggest the entrainment of another component from long‐range transport in the upper troposphere from beyond North America. In two of the case studies the export from the PBL was presumably influenced by large‐scale convection.

Forecasted deep stratospheric intrusions over Central Europe: case studies and climatologies

“…Quite frequently, layers of stratospheric air may overpass our area at about 3 km a.s.l. for several days (e.g., Trickl et al, 2003). In these cases they are observed at the Alpine summit stations during an extended period of time.…”

“…The period between February and August 2001 has been particularly successful in this regard and yielded, together with our earlier work (e.g., Eisele et al, 1999;Stohl and Trickl, 1999;Zanis et al, 2003;Roelofs et al, 2003;Trickl et al, 2003) a large variety of different cases with strongly differing complexity. The sometimes enormous number of simultaneously occurring intrusions over the North Atlantic, which may have a large impact on the STT budget, calls for a more detailed meteorological analysis, also in view of potentially changing atmospheric dynamics during the past decades (see remarks on trend studies further below).…”

“…Some details have been evaluated with the FLEXPART tracer model (Stohl et al, 1998Stohl and Thomson, 1999), operated with ECMWF re-analysis data. This model has been extensively used for transport studies, in particular for several STT case studies of our team (Stohl and Trickl, 1999;Stohl et al, 2000;Trickl et al, 2003Trickl et al, , 2009Zanis et al, 2003).…”

“…The vertical resolution is dynamically varied, roughly between 50 m and a few hundred metres, depending on the signal-to-noise ratio that decreases with altitude. The lidar has been used in numerous investigations mostly focussing on atmospheric transport (e.g., Eisele et al, 1999;Stohl and Trickl, 1999;Seibert et al, 2000;Carnuth et al, 2002;Trickl et al, 2003;.…”

35 yr of stratospheric aerosol measurements at Garmisch-Partenkirchen: from Fuego to Eyjafjallajökull, and beyond

“…The lidar system at IMK-IFU is an instrument of both NDACC and EARLINET. This system was originally built in 1973 (Impulsphysik GmbH), based on a ruby laser, and, in addition to a large number of routine and campaign-type tropospheric measurements (e.g., Reiter and Carnuth, 1975 Jäger et al, 1988Jäger et al, , 2006Forster et al, 2001;Trickl et al, 2003Trickl et al, , 2011, has been almost continually used for measurements of stratospheric aerosol since autumn 1976 (e.g., Jäger, 2005;Deshler et al, 2006;Fromm et al, 2008bFromm et al, , 2010. The lidar was converted to a spatially scanning system with a Nd:YAG laser (Quanta Ray, GCR 4, 10 Hz repetition rate, about 700 mJ per pulse at 532 nm) in the early 1990s for additional investigation of contrails (Freudenthaler, 2000;Freudenthaler et al, 1994Freudenthaler et al, , 1995.…”