Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 10269-10290, 2017
https://doi.org/10.5194/acp-17-10269-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
01 Sep 2017
Stratospheric ozone intrusion events and their impacts on tropospheric ozone in the Southern Hemisphere
Jesse W. Greenslade1, Simon P. Alexander2,3, Robyn Schofield4,5, Jenny A. Fisher1,6, and Andrew K. Klekociuk2,3 1Centre for Atmospheric Chemistry, School of Chemistry, University of Wollongong, Australia
2Australian Antarctic Division, Hobart, Australia
3Antarctic Climate and Ecosystems Co-operative Research Centre, Hobart, Australia
4School of Earth Sciences, University of Melbourne, Australia
5ARC Centre of Excellence for Climate System Science, University of New South Wales, Australia
6School of Earth & Environmental Sciences, University of Wollongong, Australia
Abstract. Stratosphere-to-troposphere transport (STT) provides an important natural source of ozone to the upper troposphere, but the characteristics of STT events in the Southern Hemisphere extratropics and their contribution to the regional tropospheric ozone budget remain poorly constrained. Here, we develop a quantitative method to identify STT events from ozonesonde profiles. Using this method we estimate the seasonality of STT events and quantify the ozone transported across the tropopause over Davis (69° S, 2006–2013), Macquarie Island (54° S, 2004–2013), and Melbourne (38° S, 2004–2013). STT seasonality is determined by two distinct methods: a Fourier bandpass filter of the vertical ozone profile and an analysis of the Brunt–Väisälä frequency. Using a bandpass filter on 7–9 years of ozone profiles from each site provides clear detection of STT events, with maximum occurrences during summer and minimum during winter for all three sites. The majority of tropospheric ozone enhancements owing to STT events occur within 2.5 and 3 km of the tropopause at Davis and Macquarie Island respectively. Events are more spread out at Melbourne, occurring frequently up to 6 km from the tropopause. The mean fraction of total tropospheric ozone attributed to STT during STT events is  ∼ 1. 0–3. 5 % at each site; however, during individual events, over 10 % of tropospheric ozone may be directly transported from the stratosphere. The cause of STTs is determined to be largely due to synoptic low-pressure frontal systems, determined using coincident ERA-Interim reanalysis meteorological data. Ozone enhancements can also be caused by biomass burning plumes transported from Africa and South America, which are apparent during austral winter and spring and are determined using satellite measurements of CO. To provide regional context for the ozonesonde observations, we use the GEOS-Chem chemical transport model, which is too coarsely resolved to distinguish STT events but is able to accurately simulate the seasonal cycle of tropospheric ozone columns over the three southern hemispheric sites. Combining the ozonesonde-derived STT event characteristics with the simulated tropospheric ozone columns from GEOS-Chem, we estimate STT ozone flux near the three sites and see austral summer dominated yearly amounts of between 5. 7 and 8. 7 × 1017 molecules cm−2 a−1.

Citation: Greenslade, J. W., Alexander, S. P., Schofield, R., Fisher, J. A., and Klekociuk, A. K.: Stratospheric ozone intrusion events and their impacts on tropospheric ozone in the Southern Hemisphere, Atmos. Chem. Phys., 17, 10269-10290, https://doi.org/10.5194/acp-17-10269-2017, 2017.
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An analysis of data from ozonesondes released at three southern oceanic sites shows the impact of stratospheric ozone in this region. Using a novel method of transport classification, this work estimates the seasonality and quantity of stratospherically sourced ozone. We find that ozone is transported most frequently in summer due to regional-scale low-pressure weather systems. We also estimate a stratospheric ozone source of 2.0–3.3 Tg/year over three Southern Ocean regions.
An analysis of data from ozonesondes released at three southern oceanic sites shows the impact...
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