A textbook example of long‐range transport: Simultaneous observation of ozone maxima of stratospheric and North American origin in the free troposphere over Europe

Abstract

Abstract. We describe an episode of a stratospheric intrusion into the free troposphere over Europe followed by a long-range transport of ozone from the North American boundary layer. Observational data showed the presence of a thin tongue of stratospheric air in the free troposphere for at least 36 hours. This filament was found in data from two ozone soundings and was recorded continuously for 26 hours by a high-resolution ozone lidar. The stratospheric air also intercepted two high Alpine summits, causing elevated ozone and beryllium 7 concentrations. Trajectory, particle dispersion model, and potential vorticity analyses confirmed the stratospheric nature of the tongue. In the lidar data, following the intrusion, pockets of elevated ozone concentrations (80-100 ppb) were found in the free troposphere close to the tropopause. The low potential vorticity values and high water vapor content in these ozone-rich pockets and trajectory analyses suggest that the ozone was photochemically produced in the boundary layer over eastern North America, followed by rapid uplifting in a warm conveyor belt over the Atlantic Ocean ahead of a frontal system. This was confirmed by ozone and water vapor measurements aboard commercial airliners crossing the warm conveyor belt. The air mass trajectories in both the stratospheric intrusion and the warm conveyor belt were tightly bundled, emphasizing the importance of the coherency of airstreams for long-range ozone transport. IntroductionOzone ( [1998] recently demonstrated the capacity of the above airstreams for causing strong gradients in trace gas concentrations near fronts. In this paper, on the basis of the example of a single episode, we explore the significance of these airstreams for long-range 0 3 transport.Mixing

Stratosphere‐troposphere exchange: A review, and what we have learned from STACCATO

“…These filaments cascade down to ever smaller scales, through the action of ''chaotic advection'' [Ottino, 1989], and interleave with tropospheric air [Appenzeller et al, 1996a]. They can subside deep into the troposphere [Stohl and Trickl, 1999], and such deep descent of stratospheric air can be associated with severe weather, particularly high wind speeds at the surface [Browning and Reynolds, 1994;Goering et al, 2001]. Finally, these structures may be destroyed by turbulence and convection.…”

“…Typically, the intruding stratospheric air forms filamentary structures, which are observed in various contexts. For instance, they appear as laminae in ozone profiles [Dobson, 1973;Reid and Vaughan, 1991], as filamentary features on water vapor satellite images [Appenzeller and Davies, 1992;Wirth et al, 1997], they are evident by ozone lidar measurements [Stohl and Trickl, 1999] and have been detected by in situ aircraft measurements [Reid and Vaughan, 1993;Balluch and Haynes, 1997;Newell et al, 1999]. These filaments cascade down to ever smaller scales, through the action of ''chaotic advection'' [Ottino, 1989], and interleave with tropospheric air [Appenzeller et al, 1996a].…”

A backward modeling study of intercontinental pollution transport using aircraft measurements

“…FLEXPART was validated with data from three large-scale tracer experiments in North America and Europe [Stohl et al, 1998], and it was used previously in case studies of ICT [Stohl and Trickl, 1999;Forster et al, 2001;Spichtinger et al, 2001] and to simulate intrusions of stratospheric air into the lower troposphere [Stohl et al, 2000]. It was also employed to develop a 1-year ''climatology'' of ICT [Stohl et al, 2002a].…”

“…[4] While the meteorological conditions favoring fast ICT are relatively well understood [Stohl and Trickl, 1999;Stohl, 2001], the chemical changes occurring in the process are much less well characterized. One reason for this is that transport to the upper troposphere takes place mostly in clouds, leading to washout of water-soluble gases and aerosols, a process which is still poorly parameterized in chemistry transport models (CTMs).…”

Peer Reviewed: Global Ozone Concentrations and Regional Air Quality

“…The mechanisms underpinning the potential increases in O 3 concentrations in Figures 1-3 Weather systems and their associated fronts in midlatitudes provide another vehicle for transporting surface-emitted pollutants to the middle and upper troposphere (9). But the missing element has been the meteorological processes that bring upper tropospheric air laden with O 3 down to the land surfaces.…”