In the austral spring seasons of 2020-2022, the Antarctic stratosphere
experienced three consecutive strong vortex events. In particular, the
Antarctic vortex of October-December 2020 was the strongest on record in
the satellite era for that season at 60°S in the mid- to lower
stratosphere. However, it was poorly predicted by the Australian Bureau
of Meteorology’s operational seasonal climate forecast system of that
time, ACCESS-S1, even at a short lead time of a month. Using the current
operational forecast system, ACCESS-S2, we have, therefore, tried to
find a primary cause of the limited predictability of this event and
conducted forecast sensitivity experiments to climatological versus
observation-based ozone to understand the potential role of the ozone
forcing in the strong vortex event and associated anomalies of the
Southern Annular Mode (SAM) and south-eastern Australian rainfall. Here,
we show that the 2020 strong vortex event did not follow the canonical
dynamical evolution seen in previous strong vortex events in spring,
whereas the ACCESS-S2 control forecasts with the climatological ozone
did, which likely accounts for the inaccurate forecasts of ACCESS-S1/S2
at 1-month lead time. Forcing ACCESS-S2 with observed ozone
significantly improved the skill in predicting the strong vortex in
October-December 2020 and the subsequent positive SAM and related
rainfall increase over south-eastern Australia in the summer of December
2020 to February 2021. These results highlight an important role of
ozone variations in seasonal climate forecasting as a source of
long-lead predictability, and therefore, a need for improved ozone
forcing in future ACCESS-S development.