deletions | additions       diff --git a/Characterisation_of_STTs.tex b/Characterisation_of_STTs.tex  index a0f3b8b..e2d7891 100644  --- a/Characterisation_of_STTs.tex  +++ b/Characterisation_of_STTs.tex 
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\subsection{Characterisation of STTs}  \label{Section:CharacterisationOfSTTs}  STTs have STT events are characterised in the vertical profiles of ozone as altitudes in the troposphere where the ozone mixing ratio exceeds  a clear effect on threshold. Usually stratospheric ozone mixes irreversibly down into the troposphere in a synoptic-scale tongue of air:  the vertical  ozoneparts per billion volume(ppbv)  profile above a grid point(henceforth observed by the ozonesonde depends upon the time in this cycle that it isobserved \citep{Sprenger2003}. As such, the altitude of the tropospheric ozone peak due to  a profile). STT event, and the amplitude of the event, above the background tropospheric ozone profile, vary in space and time.  One important factor Firstly, two definitions  ofSTT characterisation was  the tropopause  height of the tropopause, which can be defined in several ways.  Using only the ozonesonde datasets, are calculated:  the tropopause from ozone and standard WMO  lapse rate definitions are easy to calculate. tropopause \citep{WMO1957}, and the ozone tropopause (following the definition of \citep{Bethan1996}, but for Davis as modified by \citep{Tomikawa2009,Alexander2013}.  While the ozone tropopause can be less robust during stratosphere-troposphere exchange, it performs better than the lapse rate tropopause at polar latitudes in winter and near jet streams in the lower stratosphere \cite{Bethan1996}. For many The lower  of these tropopause altitudes is taken as  the sonde profiles ozone disturbances occur between the lapse rate and ozone defined tropopauses, and since tropopause for this study, because  it is not clear likely  that this area is actually mixing of minor constituents occurs in  the upper  troposphere we only characterise events bound by the and  lower of the stratosphere, particularly when there is an ill-defined  lapse rate and ozone tropopause heights. tropopause.  First the profiles are linearly interpolated to a regular grid with 20m resolution up to 14km.  Then profiles are run through a Fourier bandpass filter which removes scales outside of 0.5km and 5km, leaving us with the ozone perturbation from background.  In order to avoid spurious events caused by surface pollution or Fourier transform anomalies these perturbation profiles are trimmed to between 2km above the surface and 1km below the tropopause.  Now using all the trimmed filtered profiles we extract those with points above the 99th percentile(locally) of all ozone levels.  %STTs have a clear effect on the ozone parts per billion volume(ppbv) profile above a grid point(henceforth a profile).  %One important factor of STT characterisation was the height of the tropopause, which can be defined in several ways.  %Using only the ozonesonde datasets, the tropopause from ozone and lapse rate definitions are easy to calculate.  %While the ozone tropopause can be less robust during stratosphere-troposphere exchange, it performs better than the lapse rate tropopause at polar latitudes in winter and near jet streams in the lower stratosphere \cite{Bethan1996}.  %For many of the sonde profiles ozone disturbances occur between the lapse rate and ozone defined tropopauses, and since it is not clear that this area is actually the troposphere we only characterise events bound by the lower of the lapse rate and ozone tropopause heights.  First the vertical profiles of ozone are linearly interpolated to a regular grid with 20m resolution up to 14km and are then bandpass filtered so as to retain perturbations on altitude scales between 0.5km - 5km. The choice of band limits is set empirically, but we note that to define an STT event, a clear increase above the background ozone is needed, and a vertical limit of ($\sim 5$~km) removes seasonal-scale effects \textbf{SA: to reword and make clearer...}. The ozone perturbation profile is then considered at altitudes from 2~km above the surface (to avoid surface pollution events) and 1~km below the tropopause (to avoid the sharp transition to stratospheric air producing spurious false positives). Perturbations above the 99~th percentile (locally) of all ozone levels are initially classified as potential STT events.  %Then profiles are run through a Fourier bandpass filter which removes scales outside of 0.5km and 5km, leaving us with the ozone perturbation from background.  %In order to avoid spurious events caused by surface pollution or Fourier transform anomalies these perturbation profiles are trimmed to between 2km above the surface and 1km below the tropopause.  %Now using all the trimmed filtered profiles we extract those with points above the 99th percentile(locally) of all ozone levels.  In order to remove unclear 'near tropopause' anomalies we further filter out events where the gradient between the maximum ozone peak and the tropopause minus 1km altitude at 1~km below the  is greater than -20 ppbv/km as and require that the perturbation profile not drop below zero between the event peak and the tropopause. %as  well as having the Fourrier filtered profile not drop below zero between the event peak and the tropopause. \subsection{Conservative estimate of ozone flux}