Multiple large-scale dynamical pathways for pan--Atlantic compound cold and windy extremes

• Main Authors: Riboldi, Jacopo, Leeding, Richard, Segalini, Antonio, Messori, Gabriele
• Format: Other/Unknown Material
• Language: unknown
• Published: Authorea, Inc. 2022
• Subjects: Pacific; North Atlantic
• Online Access: http://dx.doi.org/10.22541/essoar.167108815.57535236/v1

Winter cold spells over North America have been correlated with European wind extremes, but the physical mechanisms behind such “pan-Atlantic” compound extremes have not been clarified yet. In this study, we propose that pan–Atlantic cold and windy extremes occur following two possible dynamical pathways. The first one involves the propagation of a Rossby wave train from the Pacific Ocean, associated with windstorms over north-western Europe in the 5-10 days after the cold spell peak. The second is associated with a high-latitude anticyclone over the North Atlantic and an equatorward-shifted jet, leading to windstorms over south-western Europe already in the days preceding the cold spell peak. European windstorms are thus consistently tied to North American cold spells according to the different flow configuration. The analysis underscores that seemingly similar surface extremes may be driven by different processes, and that overlooking these subtleties and conflating them together could lead to misleading conclusions.