From Atmospheric Waves to Heatwaves: A Waveguide Perspective for Understanding and Predicting Concurrent, Persistent, and Extreme Extratropical Weather

Abstract

A notable number of high impact weather extremes have occurred in recent years, often associated with persistent, strongly meandering atmospheric circulation patterns known as Rossby waves. Because of the high societal and ecosystem impacts, it is of great interest to be able to accurately project how such extreme events will change with climate change, and to predict these events on seasonal to subseasonal (S2S) timescales. There are multiple physical links connecting upper atmosphere circulation patterns to surface weather extremes, and it is asking a lot of our dynamical models to accurately simulate all of these. Subsequently, our confidence in future projections and S2S forecasts of extreme events connected to Rossby waves remains relatively low. We also lack full fundamental theories for the growth and propagation of Rossby waves on the spatial and temporal scales relevant to extreme events, particularly under strongly non-linear conditions. By focussing on one of the first links in the chain from upper atmospheric conditions to surface extremes -- the Rossby waveguide -- it may be possible to circumvent some model biases in later links. To further our understanding of the nature of waveguides, links to persistent surface weather events and their representation in models, we recommend: exploring these links in model hierarchies of increasing complexity, developing fundamental theory, exploiting novel large ensemble data sets, harnessing deep learning, and increased community collaboration. This would help increase understanding and confidence in both S2S predictions of extremes and of projections of the impact of climate change on extreme weather events.

Accelerated western European heatwave trends linked to more-persistent double jets over Eurasia

“…The double jet configuration can provide the necessary latitudinal waveguide via a confined subtropical jet 43 that traps and amplifies Rossby waves. Such states have been identified for extreme summer months 44 . As we show in our analysis, double jets are associated with a strong and confined subtropical jet (favoring waveguidability) and amplified circumglobal wave patterns in the meridional wind.…”

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

“…The role of QRA in the recurrence of Rossby waves also needs to be investigated further. Investigating the role of background flow is not straightforward because defining it is a formidable problem (Wirth et al, 2018; see discussions in White et al, 2021). The interaction of RRWPs with other well-known climate oscillation patterns also needs to be investigated further.…”

Projected changes in early summer ridging and drought over the Central Plains

“…Finally, we note that the approach we have taken in this study, where we analyzed drought during specified circulation anomalies under different warming levels, could easily be applied and informative for other regions and extreme events. Most climate extremes are associated with large-scale, often intense and persistent atmospheric circulation patterns (Seager et al 2015, Tomczyk and Bednorz 2016, Breugem et al 2020, Kautz et al 2022, White et al 2022. But even while atmospheric circulation responses to warming remain highly uncertain (Li et al 2018, Huguenin et al 2020, circulation variability itself will still play a critical role in the occurrence of climate extremes in the future (Mankin et al 2020).…”