Current and projected changes in the southern hemisphere UTLS ozone and effects of bushfire smoke aerosols

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Molecular Science, College of Science, Health and Engineering, La Trobe University, Bundoora.

An analysis of future projections of ozone levels over Antarctica from coupled chemistry climate models (CCMVal-2) using multi-model median (MMM) trends found that the Antarctic Total Ozone Column (TOC) will not return to 1965 values during the September-November months by the end of the 21st century and that December TOC will not return to that baseline until 2080. The rate of TOC recovery during December was slower than for austral spring, due to a delayed increase of ozone at 50-100 hPa. At these altitudes, MMM temperature trends were projected to stop increasing by 2060 due to the combined radiative effect of a projected increase in greenhouse gases (GHG) and a decrease in ozone depleting substances. A persisting polar vortex was projected until the middle of the 21st century during December in the lower stratosphere. Seasonal TOC zonal asymmetry patterns are analysed, with MMM seasonal trends during the observation period (1979-2005) showing reduced amplitudes and smaller eastward phase trends in TOC compared with satellite observations during austral spring. Fourier decomposition of MMM TOC trends show that the QSW-wave 1 harmonic is dominant during austral spring at Antarctic latitudes, indicating reduced tropospheric planetary wave forcing. There is qualitative agreement between eastward phase trends over Antarctica and model simulations during the ozone depletion period which then reverses with increasing ozone during the 21st century. A residual eastward phase trend towards the end of the century in both seasons is observed, suggesting a long-term phase shift in TOC distribution due to changes in GHGs and ozone depletion. Limb-scattered radiance data was used to monitor the pyrocb event from the 2009 Black Saturday bushfire as it was transported into the lower stratosphere, reaching altitudes of at least 21 km. The smoke plume dispersed over time and circled the globe in about 6 weeks, with smoke aerosols present in the lower stratosphere for approximately 3 months. Water vapour was entrained with the smoke plume from the upper troposphere, hydrating the dry lower stratosphere over latitudes of approximately 10-40◦S. Water vapour perturbations were observed for at least 3 weeks after bushfire ignition from two sets of satellite measurements. Additionally, the smoke plume also transported ozone-poor air from the troposphere into the lower stratosphere, providing localised ozone depletion for at least 4 weeks up to the lower boundary of the Brewer Dobson Circulation. Such chemical perturbations have not been observed previously in relation to a pyrocb event.