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%In the troposphere ozone is a trace gas mostly generated by photochemistry, due to both pollution and natural processes.   %Stratosphere to Troposphere Transport of ozone events(STTs) are a relatively small source of tropospheric ozone, however the regional %effect can be quite large and the dynamics which cause these events are not perfectly understood \cite{Mihalikova2012,Zhang_2014}.  Ozone is present in the troposphere due to a variety of dynamical and photochemical processes, including downward transport from the ozone-rich stratosphere and anthropogenic pollution. Ozone-rich air mixes irreversibly down from the stratosphere during meteorologically conducive conditions \cite{Sprenger2003,Milhalikova2012}; \cite{Sprenger2003, Mihalikova2012};  these are referred to as Statosphere - Troposphere Transport (STT) events. In the extra-tropics, STT most commonly occurs during synoptic-scale tropopause folds \cite{Sprenger2003} and are characterised by tongues of high PV air descending to low altitudes. These tongues become elongated and filaments separate from the tongue which mix into tropospheric air. Stratospheric ozone brought deeper (lower) into the troposphere is more likely to affect the surface ozone budget and tropospheric chemistry \cite{Zanis2003}. While the amount of tropospheric ozone is small compared with that found in the stratosphere, it is an important constituent \textbf{XXXX - Robyn please add some chemistry stuff here...}. The relative contributions to the tropospheric ozone budget of photochemistry and STT (dynamical transport) is still uncertain \cite{Zanis2003}.  
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%Examine the coincidental weather and determine possible causes or necessary conditions of an event over the three southern hemisphere sites.  %We also examine seasonality and look at the distributions of ozone intrusions classified by intrusion depth.