On the relation between explosive cyclones affecting Europe and the North Atlantic Oscillation

Abstract

Intense winter cyclones often lead to hazardous weather over Europe. Previous studies have pointed to a link between the North Atlantic Oscillation (NAO) and strong European windstorms. However, the robustness of this relation for cyclones of varying intensities remains largely unexplored. In this paper, the bi-directional relation between the NAO and cyclones impacting Europe is analyzed for the period 1950-2010 focusing on the sensitivity to storm intensity. Evidence is given that explosive (EC) and non-explosive cyclones (NoEC) predominantly develop under different large-scale circulation conditions over the North Atlantic. Whereas NoEC evolve more frequently under negative and neutral NAO phases, the number of EC is larger under a positive NAO phase, typically characterized by an intensified jet toward Western Europe. Important differences are also found on the dynamics of NAO evolution after peak intensity for both cyclone populations.

Dynamical proxies of North Atlantic predictability and extremes

“…A positive NAO favours the occurrence of cyclones across the North Atlantic14 and destructive surface winds over continental Europe15. Indeed, we find a match between low instaneous dimensions and historical storms: the names and dates of storms corresponding to minima of d ( ζ ) are reported in Fig.…”

On cold spells in North America and storminess in western Europe

“…Statistically significant increases in destructiveness rates are found at both positive and negative lags; the peak composite PDI value exceeds 11% (Figure 2c). We note that this value is well in excess of that associated with the positive NAO (Table 1), which is often linked to enhanced storminess over the Atlantic [e.g., Gómara et al, 2014b]. The origin of the double peak in the PDI index is discussed in detail in Text S6.…”

“…Cold temperatures over North America and storms affecting Europe are often discussed in the context of the Pacific-North American Pattern (PNA) and the NAO [e.g., Leathers et al, 1991;Gómara et al, 2014b]. Here we investigate whether the large-scale patterns and anomaly fields discussed in section 3 are the direct results of strong projections on either of these variability patterns.…”

On double Rossby wave breaking in the North Atlantic

“…In view of this, one might naively expect DWB to have a strong connection with the leading mode of climate variability in the region, namely, the NAO. The NAO has been repeatedly investigated as a major driver of both Atlantic storminess and jet stream anomalies [e.g., Woollings and Blackburn , ; Pinto and Raible , ; Gómara et al , ]. It has also been interpreted as the outcome of specific WB configurations [e.g., Benedict et al , ; Franzke et al , ; Riviere and Orlanski , ; Strong and Magnusdottir, , ; Kunz et al , ; Drouard et al , ], and WB frequency over localized regions of the North Atlantic has been found to account for a very high fraction of both the interannual and intraseasonal NAOI variability [ Strong and Magnusdottir , ].…”

“…The DWB described in section 3 is a large‐scale process, with individual events spanning a vast stretch of the North Atlantic basin. Previous studies have suggested that the occurrence of Rossby wave breaking, especially if associated with a positive NAO, has a strong influence on the jet stream [ Riviere and Orlanski , ; Gómara et al , ; Pinto et al , ]. As discussed in section 1, DWB will generally lead to an increased meridional PV gradient in the region between the breakings and to an intensified midlatitude jet.…”