Abstract
In the year 2025, recovery of the Antarctic ozone hole in response to the Montreal Protocol is underway. However, improvement is slow, and the ozone hole is expected to remain a yearly phenomenon for decades to come. Twenty years after the turnaround in stratospheric chlorine levels, recovery signals are mixed amongst natural variability. Some of the largest and longest-lived ozone holes on record have occurred within the last five years. Such variability has significant consequences to regional scale climate, as deep polar ozone loss leads to circulation changes which propagate across the entire Southern Hemisphere.
This thesis begins with an updated long term trend assessment of polar ozone observations. The assessment finds evidence supporting ongoing chemical recovery, however, it also uncovers a previously unreported dynamical mechanism which may be responsible for maintaining longer-lived ozone holes in recent years. After investigating this dynamical mechanism further, physical links are found between wave propagation, polar vortex conditions, descent from the mesosphere into the polar vortex, and horizontal ozone transport. To quantify the contribution of dynamics to springtime ozone columns, a novel diagnostic metric and a new mesospheric descent classification system is developed. The months leading up to the austral spring are then retrospectively probed for observational signatures which precede long-lived ozone holes. A pathway of dynamical preconditioning begins to emerge five months prior to uniquely long-lived ozone holes, sometimes following volcanic activity. Signatures along this pathway can be harnessed to produce seasonal-scale predictions for springtime ozone hole outcomes.
The outcome of the research in this thesis is a significantly improved ability to predict and diagnose both past and future Antarctic ozone hole conditions. Triggering events, which may include volcanic eruptions or anthropogenic
emissions of sulfur aerosols, have the potential to drive the Southern Hemisphere towards the dynamical pathway identified in this work. The future frequency of this preconditioned atmospheric mode, and thus long-lived ozone holes, remains unknown. In light of upcoming ‘data deserts’ in satellite observations, ongoing research into Antarctic ozone will remain important for weather and climate preparedness efforts across New Zealand and Australia.