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The primary sources of tropospheric ozone are chemical creation and stratospheric input, estimated using a model ensemble to be $5100\pm600 Tgyr^{-1}$ and $550\pm170 Tgyr^{-1}$, respectively.  The primary sinks are chemical destruction and dry deposition, estimated to be $4700\pm700 Tgyr^{-1}$ and $1000\pm200 Tgyr^{-1}$, respectively \cite{Stevenson_2006}.  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, Mihalikova2012}; \cite{Sprenger2003,Mihalikova2012};  these are referred to as Statosphere - Troposphere Transport events (STTs). In the extra-tropics, STTs most commonly occur during synoptic-scale tropopause folds \cite{Sprenger2003} and are characterised by tongues of high Potential Vorticity (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, Zhang_2014}. \cite{Zanis2003,Zhang_2014}.  While the amount of tropospheric ozone is small compared with that found in the stratosphere, it is an important constituent. The relative contributions to the tropospheric ozone budget of photochemistry and STT (dynamical transport) is still uncertain \cite{Zanis2003, paper \cite{Zanis2003,paper  in open tab}. A high correlation is found between lower stratospheric and tropospheric ozone \cite{Terao_2008} with the highest STT associated with the jet-streams over the oceans in winter.  Irreversible STT of ozone have been shown to be important for explaining tropospheric ozone variability \cite{Tang_2011}.