4.1 Simulation of the Egbert 2009 Ozonesonde Campaign
4.1.2 Backward Simulation
Backward time particle simulations enable the implementation of a source-receptor relationship that defines upstream influences on tracer observations at the receptor. It helps derive areas of influence that provide quantitative measures of the effects of different emissions on the air quality at receptor sites. Backward simulations with the particle model were introduced as an indispensable tool for a more detailed analysis of the source region of the observed enhanced ozone.
A total of 600,000 particles were released at the receptor, i.e., along a vertical line which spans the height range of enhanced ozone. As can be seen from Figure 4.3, low relative humidity and high ozone concentration is observed in the height range between 7.2 and
7.3 km so the receptor will be along a 79.73oW) on 10 May 2009 between for the previous 60 hours.
Figure 4.3. Ozonesonde measurement at Egbert on
UTC launch time. Particles release height and time was determined from launch time and the height where enhanced ozone concentration was observed. Accordingly, the particles were released on 10
height range between 7200
Signatures of the presence of stratospheric air in the lower troposphere are found for all profiles on 8 – 11 May. Figure 4.3 is one of the ozone height profiles which shows a distinct layer in the upper troposphere, i.e., in the height range between 7.2 and 7.3 km, with very low relative humidity and high
ptor will be along a line between 7 and 7.5 km at Egbert (44.27 on 10 May 2009 between 9 - 12 UTC) and it is transported backward in time
.
. Ozonesonde measurement at Egbert on 10 May 2010 at around 11:00 UTC launch time. Particles release height and time was determined from launch time and the height where enhanced ozone concentration was observed. Accordingly, the particles were released on 10th May 2009 during 9 –
height range between 7200 – 7300 m and at Egbert (44.27°N, 79.73°W).
Signatures of the presence of stratospheric air in the lower troposphere are found for all 11 May. Figure 4.3 is one of the ozone height profiles which shows a ct layer in the upper troposphere, i.e., in the height range between 7.2 and 7.3 km, with very low relative humidity and high‐ozone mixing ratio at the Egbert station km at Egbert (44.27oN, ) and it is transported backward in time
10 May 2010 at around 11:00 UTC launch time. Particles release height and time was determined from launch time and the height where enhanced ozone concentration was observed. – 12 UTC, in the 7300 m and at Egbert (44.27°N, 79.73°W).
Signatures of the presence of stratospheric air in the lower troposphere are found for all 11 May. Figure 4.3 is one of the ozone height profiles which shows a ct layer in the upper troposphere, i.e., in the height range between 7.2 and 7.3 km, ozone mixing ratio at the Egbert station
(Ontario, Canada) on 10 May. This is a partial indicator that the ozone originated in the stratosphere. However, GEM-FLEXPART numerical modeling is required to clearly confirm its stratospheric origin. The back-trajectory numerical simulation was performed employing GEM-FLEXPART and the result is indicated in Figure 4.4.
Figure 4.4. GEM-FLEXPART back-trajectories of the last 60 hours of 600,000 particles released from a line between 7 and 7.5 km at Egbert (44.27oN, 79.73oW) from 9 – 12 UTC. The black plus sign shows Egbert radar and ozonesonde launching site. The trajectories’ colours, coded as in the label bar, refer to their actual altitude.
Figure 4.4 shows the origin and pathways of the air mass leading to the observed ozone enhancement in the upper troposphere (7.2 – 7.3 km above the ground) on 10th May 2009. The GEM-FLEXPART model, which was run in backward mode, takes into account both resolved motions and parameterized subgrid scale convection and
turbulence, using the same parameterizations as the forward model mentioned in chapter 2. The FLEXPART calculations of complex output can be compressed through clustering particles into a number of clustered positions during each output [Stohl et al., 2002]. Cluster is defined as grouping of similar trajectories during a specific time. Figure 4.4 shows the cluster back trajectories of the previous 60 hours preceding the release of the particles. In our case, the cluster parameter is 4. Variation of altitude along a given trajectory is shown by color coding, whose scale is displayed at right side of the plot. From the backward GEM-FLEXPART simulations shown in Figure 4.4, one can clearly see that the ozone rich dry air in part came from west of Egbert. Hence, the high ozone concentration in the upper troposphere seen on 10th May 2009 at Egbert partially originated from transport from the stratosphere over the west of Egbert and blew with the wind horizontally. Our analysis of radar measurement of horizontal wind velocity (not shown in this thesis) indicates that the wind was dominantly blowing eastward, which reaffirms that the high ozone concentration at Egbert may have been in part the result of ozone which came from west of Egbert.
Even though it is believed that the long range ozone transport amplifies the amount of the observed ozone rich dry air in Figure 4.3, a considerable part of the observed enhanced dry ozone originated from the transport of ozone from the stratosphere to the troposphere. Figures 4.1 and 4.2 are clear evidence because both show the stratospheric ozone intrusion over Egbert. Furthermore, the apparent tropopause heights jump on 6th and 9th of May are also a partial indicator that the stratospheric ozone intrusion did indeed take place.
Ozonesonde measurements of low relative humidity and high ozone concentrations (see Figure 3.2) and GEM-FLEXPART numerical modeling (see Figures 4.1 – 4.4) and rapid radar derived tropopause height ascents (Figure 3.1), all suggest that stratospheric ozone intrusion events occurred on 8 – 11 May 2011. The atmospheric dynamics that cause the intrusions of stratospheric ozone at Egbert have been dealt with in depth in chapter 3 section 3.1. Indeed, determining the responsible dynamical factor that leads to stratospheric ozone intrusion is the main focus of this thesis and is mentioned there.