Rossbywellenpakete im Klimawandel und Auswirkungen auf Wetterextreme in Europa
Zusammenfassung der Projektergebnisse
The main goal of this project was to improve our understanding of multi-decadal trends and variability in the extratropical upper-tropospheric circulation and their implications for weather extremes in Europe. To this end, reanalysis data as well as historical and future climate model projections were employed. In addition, recently-developed diagnostics of local in space and time Rossby Wave Packet (RWP) properties were utilised in a way that uncovered regional variations in the long-term evolution of the extratropical circulation and its role in present or future weather extremes. During the past four decades, the amplitude of RWPs exhibited positive trends in many parts of the Northern Hemisphere extratropics during winter and negative trends during summer. At the same time, the Southern Hemisphere extratropics featured a poleward shift in the band of climatologically maximum amplitude values in summer, widespread positive amplitude trends in autumn, as well as positive phase speed trends in large parts of the extratropics in summer and autumn. Moreover, significant shifts in the occurrence of troughs and ridges (i.e., the phase of RWPs) emerged in the Northern Hemisphere during spring and summer. Finally, it was shown that many parts of the N Pacific and N America experience a shift to increasing occurrence of largeamplitude and/or quasi-stationary RWPs in winter during 1999-2019; a manifestation of the pronounced interannual-to-decadal variability that characterises the RWP amplitude and phase speed distributions in some areas and seasons. Under a high greenhouse gas emission scenario (RCP8.5), most members of the CESM-LE climate model agree that an increase in RWP amplitude and blocking frequency is expected for most of Europe in winter. The variability between the members, which was more pronounced in the case of blocking, signifies the natural internal variability that stems from the chaotic nature of the extratropical circulation. It was found that in some areas of the globe, some seasons and for some RWP properties internal variability overshadows the forced signal from the rise in greenhouse gases thus deeming regional climate projections highly uncertain. Finally, investigating the physical processes that gave rise to past temperature and precipitation extremes in Europe, as well as the role of RWPs, offered valuable insights regarding their evolution at weather time scales. Building on that and the previous results, hypotheses can be formulated about the future characteristics and occurrence frequency of these extremes under a highemission scenario. The analyses and tools designed in this project will hopefully prove useful and provide guidance in open questions regarding the future extratropical circulation and weather extremes as well as in unravelling the corresponding uncertainties in climate predictions.
Projektbezogene Publikationen (Auswahl)
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Extreme precipitation events over northern Italy. Part II: Dynamical precursors. Quarterly Journal of the Royal Meteorological Society, 147(735), 1237-1257.
Grazzini, Federico; Fragkoulidis, Georgios; Teubler, Franziska; Wirth, Volkmar & Craig, George C.
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Decadal variability and trends in extratropical Rossby wave packet amplitude, phase, and phase speed. Weather and Climate Dynamics, 3(4), 1381-1398.
Fragkoulidis, Georgios
