14 Jan 2022

14 Jan 2022

Review status: this preprint is currently under review for the journal WCD.

Recurrent Rossby waves during Southeast Australian heatwaves and links to quasi-resonant amplification and atmospheric blocks

S. Mubashshir Ali1, Matthias Röthlisberger2, Tess Parker3, Kai Kornhuber4, and Olivia Martius1,5 S. Mubashshir Ali et al.
  • 1Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Bern, Switzerland
  • 2Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
  • 3School of Earth, Atmosphere and Environment, Monash University, Clayton VIC, Australia
  • 4Earth Institute, Columbia University, New York City, NY, USA
  • 5Mobiliar Lab for Natural Risks, University of Bern, Bern, Switzerland

Abstract. In the Northern Hemisphere, recurrence of transient Rossby wave packets over periods of days to weeks, termed RRWPs, may repeatedly create similar weather conditions. This recurrence leads to persistent surface anomalies and high-impact weather events. Here, we demonstrate the significance of RRWPs for persistent heatwaves in the Southern Hemisphere (SH). We investigate the relationship between RRWPs, atmospheric blocking, and amplified quasi-stationary Rossby waves with two cases of heatwaves in Southeast Australia (SEA) in 2004 and 2009. This region has seen extraordinary heatwaves in recent years. We also investigate the importance of transient systems such as RRWPs and two other persistent dynamical drivers: atmospheric blocks and quasi-resonant amplification (QRA).

We further explore the link between RRWPs, blocks, and QRA in the SH using the ERA-I reanalysis dataset (1979–2018). We find that QRA and RRWPs are strongly associated: 40 % of QRA days feature RRWPs, and QRA events are 13 times more likely to occur with an RRWPs event than without it. Furthermore, days with QRA and RRWPs show high correlations in the composite mean fields of upper-level flows, indicating that both features have a similar hemispheric flow configuration. Blocking frequencies for QRA and RRWP conditions both increase over the south Pacific Ocean but differ substantially over parts of the south Atlantic and Indian Ocean.

S. Mubashshir Ali et al.

Status: open (until 25 Feb 2022)

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S. Mubashshir Ali et al.

S. Mubashshir Ali et al.


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Short summary
Persistent weather can lead to extreme weather conditions. One such atmospheric flow pattern, termed Recurrent Rossby wave packets (RRWPs), increases persistent weather in the Northern Hemisphere. Here, we show that RRWPs are also an important feature in the Southern Hemisphere. We evaluate the role of RRWPs and other atmospheric features during Southeast Australian heatwaves. We also study how RRWPs are related to other atmospheric features well-known for increasing heatwaves.