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.
Highlights
25 Since 1900, extreme heat has been responsible for more fatalities in Australia than all other natural hazards combined (Coates et al, 2014)
Recurrent Rossby wave packets” (RRWPs) have a significant effect on the duration of hot spells in several regions within the Southern Hemisphere (SH) and in particular over south-eastern Australia (SEA) (Fig. 4)
The regression analysis shows that RRWPs are an important feature in the SH as well: RRWPs increase the duration of hot spells in several regions over land, including SEA; the analysis does not provide any information about how frequently RRWPs and SEA heatwaves coincide
Summary
25 Since 1900, extreme heat has been responsible for more fatalities in Australia than all other natural hazards combined (Coates et al, 2014). Several large-scale atmospheric mechanisms and phenomena have been identified as potential drivers of heatwaves in the extra-tropics. These include blocking anticyclones (e.g., Barriopedro et al, 2011; Drouard and Woollings, 2018), amplified quasi-stationary waves (Teng et al, 2016; Kornhuber et al, 2020), and recurrent Rossby wave patterns (Röthlisberger et al, 2019). These phenomena have mainly been studied in isolation. 35 we focus on these three large–scale dynamical drivers of heatwaves to explore their relative importance, co-occurrence, and potential interactions during heatwaves in south-eastern Australia (SEA)
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