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Predictability of the 2020 Antarctic strong vortex event and the role of ozone forcing
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  • Eun-Pa Lim,
  • Linjing Zhou,
  • Griffith A Young,
  • Abhik Santra,
  • Irina Rudeva,
  • Pandora Hope,
  • Matthew Comstock Wheeler,
  • Julie M. Arblaster,
  • Harry H. Hendon,
  • Gloria L Manney,
  • Seok-Woo Son,
  • Jiyoung Oh
Eun-Pa Lim
Bureau of Meteorology (Australia)

Corresponding Author:eun-pa.lim@bom.gov.au

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Linjing Zhou
Bureau of Meteorology
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Griffith A Young
Bureau of Meteorology
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Abhik Santra
Bureau of Meteorology, Melbourne, Australia
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Irina Rudeva
Bureau of Meteorology
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Pandora Hope
Bureau of Meteorology
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Matthew Comstock Wheeler
Bureau of Meteorology (Australia)
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Julie M. Arblaster
Monash University
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Harry H. Hendon
Bureau of Meteorology
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Gloria L Manney
Northwest Research Associates
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Seok-Woo Son
Seoul National University
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Jiyoung Oh
Seoul National University
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Abstract

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.