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Ozone intrusions from the stratosphere to the troposphere occur as part of the Brewer-Dobson circulation, but the details of the microphysics of the process are unresolved. This research mainly focuses on near-tropopause regions, and examines stratospheric ozone intrusions into the troposphere across this stable zone. My research objective is to identify the small-scale atmospheric dynamical features responsible for the intrusion of stratospheric ozone into the troposphere, and to determine their relative importance from case to case. Windprofiler radars, together with frequent ozonesonde launches, have been used to detect stratospheric ozone intrusions. This work has been supplemented by numerical simulation via GEM-FLEXPART to unambiguously confirm the leakage. We have identified stratospheric ozone intrusion occurrence at the measurement site, and/or in some cases at some distance from the measurement site. In the latter case, ozone reaches the radar site after being blown horizontally with the wind. We have diagnosed radar measurements of the standard deviation of the vertical wind, vertical shear of the horizontal wind, and turbulence strengths, as possible indicators of small-scale atmospheric activity. Increases in the standard deviation of the vertical wind are considered to indicate enhanced gravity wave activity, and enhancements in wind shear are taken to indicate increases in small-scale dynamics (including gravity wave activity). The study shows frequent strong correlation between intrusion events and strong atmospheric activity. The atmospheric dynamics responsible for the intrusion of stratospheric ozone varies from case to case. On the one hand, we see that all parameters can act simultaneously, which clearly amplifies the intrusions. On the other hand, we see either one or any combination of the parameters acting to cause intrusions. However, the Eureka 2008 and Montreal 2005 (on 9th May) campaigns are exceptional cases where we do not see any strong atmospheric activity. We have also modeled atmospheric diffusion and examined the differences due to homogeneous turbulence compared with turbulence that is spatially and temporally intermittent. This unique combination of observational and numerical modeling helps detect the sources and sinks of ozone-related atmospheric pollutants that have negative impact on air quality, climate change and ozone depletion.

We investigated an unusual elevated-ozone episode that took place at a high altitude measuring site Zavižan (44.817°N, 14.983°E, 1594 m a.s.l.). The episode was characterized by three consecutive peaks. The first one was the highest (over 120 ppbv), and it occurred at the late night on 17 July. Following two (both about 110 ppbv) appeared approximately 18 and 36 hours after the first peak, respectively. The night-time maximum and the departure from the usual diurnal variation of ozone concentration during investigated episode point to the non-local pollution sources, rather than to local photochemical production. Thus, recorded ozone peaks might arise due to the long-range transport of photo-oxidants ; 2) stratospheric ozone intrusion ; or 3) they might be result of both (1) and (2). In order to inspect which of above processes is responsible for the increased ozone concentrations we applied the unified EMEP model, which among others, simulates atmospheric transport and deposition of photo-oxidants, and, a mesoscale numerical weather prediction model WRF-ARW V2.2. Additionally, the larger scale atmospheric conditions were examined based on the ECMWF ERA-40 reanalysis fields. Results suggest that the stratospheric ozone intrusion played an important role in the occurrence of investigated episode.

We investigated an unusual elevated-ozone episode that took place at a high altitude measuring site Zavižan (44.817°N, 14.983°E, 1594 m a.s.l.). The episode was characterized by three consecutive peaks. The first one was the highest (over 120 ppbv), and it occurred at the late night on 17 July. Following two (both about 110 ppbv) appeared approximately 18 and 36 hours after the first peak, respectively. The night-time maximum and the departure from the usual diurnal variation of ozone concentration during investigated episode point to the non-local pollution sources, rather than to local photochemical production. Thus, recorded ozone peaks might arise due to the long-range transport of photo-oxidants; 2) stratospheric ozone intrusion; or 3) they might be result of both (1) and (2). In order to inspect which of above processes is responsible for the increased ozone concentrations we applied the unified EMEP model, which among others, simulates atmospheric transport and deposition of photo-oxidants, and, a mesoscale numerical weather prediction model WRF-ARW V2.2. Additionally, the larger scale atmospheric conditions were examined based on the ECMWF ERA-40 reanalysis fields. Results suggest that the stratospheric ozone intrusion played an important role in the occurrence of investigated episode.

[1] We investigated mesoscale meteorological conditions in the lower troposphere during an episode of winter stratospheric ozone intrusion over Zagreb, Croatia, on 6 February 1990. This particular event was associated with a jet stream over northwestern Europe, and it was accompanied by elevated ozone values at two measuring sites in the greater Zagreb area. A Eulerian nonhydrostatic prognostic mesoscale model has been employed to reproduce significant fine-scale features of the fold. The initial streamer of the potential vorticity (PV) anomaly, which was found in the lower troposphere from 1.5 to 1 day prior to measured ozone peaks, consisted of a wavelike train of vortices. Horizontal and vertical dimensions of the individual vortices were between 30 and 70 km and between 500 and 1500 m, respectively. At the same time, the vertical PV gradients within the vortices were up to Δ PV = 0.2 × 10− 6 K m Pa− 1 s− 3/100 m. The model also reproduced the streamer's breaking apart and its gradual and irreversible mixing with the adjacent tropospheric air. Both the model results and ozone measurements suggest that the air of stratospheric origin arrived above Zagreb from the southeast.