On the connection between Rossby waves and spatially compounding weather extremes

When different weather extremes occur at multiple locations at the same time, their aggregated impact can exceed the one of the individual events. Examples can be concomitant summer heatwaves over major breadbasket regions, leading to potential food shortages at the global scale, or the connection between cold spells over North America and windstorms over Europe. These compound events often attract a broad interest by the media and society, as anomalous weather conditions seem to occur “everywhere at the same time”. If it is possible to identify a physical linkage between them, those separate extremes can be considered as parts of a single, spatially compounding weather extreme. Pinpointing a common physical driver is not trivial, however, and it might well be that such extreme events just co-occur by coincidence.This overview presentation will discuss how the linear and nonlinear dynamics of Rossby waves can help to understand spatially compounding extremes. Examples of linear dynamics involve the propagation of Rossby wave packets across broad portions of the middle latitudes, aided by the presence of upper-level waveguides. The link between extreme weather and atmospheric blocking, on the other hand, can be seen as involving a nonlinear sort of dynamics. Analytical, idealized and data-driven approaches to the study of Rossby waves can shed light on the drivers of spatially compounding extremes, and result in useful tools to study how the drivers of such extremes are being affected by anthropogenic global warming.