On the low-frequency variability of wintertime Euro-Atlantic planetary wave-breaking

Abstract

Planetary wave-breaking can lead to large-scale atmospheric circulation anomalies and favour high-impact weather occurrences. For example, the simultaneous occurrence of anti-cyclonic wave-breaking to the south of the North Atlantic jet and cyclonic wave-breaking to the north, here termed double wave-breaking, has been linked to heightened frequencies of explosive cyclones in the Atlantic basin and destructive windstorms over Western and Continental Europe. The present study analyses the long-term temporal variability of wintertime cyclonic and anti-cyclonic wave-breaking, and the resulting double wave-breaking, in the North Atlantic. We use reanalysis data, proxy reconstructions of the North Atlantic Oscillation (NAO) and a 1000-year coupled global climate model equilibrium simulation under constant pre-industrial forcing. The wave-breaking wavelet spectra highlight a significant ultra-centennial variability in double wave-breaking frequency, which is largely mirrored in the variability of the NAO. However, we note that the NAO wavelet spectra in the different datasets display significant discrepancies. The low-frequency wave-breaking variability is reflected in long-term anomalies of the large-scale atmospheric circulation in the Euro-Atlantic sector. The 100-year periods with the most and least double wave-breaking occurrences display significant and opposite anomalies in both upper and lower-level wind, as well as in the frequency of extreme temperature events and in the magnitude of wind destructiveness over Europe. The latter broadly resembles the wind destructiveness anomalies associated with individual double wave-breaking instances in reanalysis data. The existence of low-frequency variability in an atmospheric pattern related to high-impact weather events has important implications for the study and interpretation of climate change projections and of possible future NAO changes.

A Synoptic Scale Perspective on Greenland Ice Core δ18O Variability and Related Teleconnection Patterns

“…On the western side of the RWB pattern a filament of increased moisture transport occurs, leading to moist and warm conditions in southern, western and central Greenland, i.e., more positive δ 18 O in ice core records. This is consistent with previous studies [1], which report a significant negative correlation between the NAO, which is negatively correlated with RWB activity in the North Atlantic [10], and southern and central Greenland ice core δ 18 O. The increase in the frequency of cold events over Europe during high ice core δ 18 O winters is related to the increase in the frequency of cold polar air advected towards south on the eastern part of the RWB pattern.…”

“…Overall, extreme WVT into the Arctic region is associated with blocking-like atmospheric circulation patterns [8], which are closely related to Rossby wave breaking (RWB) [9]. RWB, commonly defined as the large-scale, irreversible overturning of potential vorticity contours near the tropopause level, can lead to large-scale atmospheric circulation anomalies with significant impact on synoptic-scale patterns [10]. Persistent wave-breaking events are associated with atmospheric blocking [11].…”

Compound Climate Events and Extremes in the Midlatitudes: Dynamics, Simulation, and Statistical Characterization

“…A zonal, intense jet also leads to heavy precipitation, associated with the Atlantic cyclones, and favours the penetration of warm, moist airmasses deep into the European continent. The above process chain is recovered when studying multidecadal or longer variability in long climate model integrations (Messori et al, 2019). This has important implications for the interpretation of dynamical changes in climate projections and their relevance for high-impact compound climate extremes in Europe.…”

“…Europe (e.g. Messori et al, 2019;De Luca et al, 2020a). Gabriele Messori discussed the causal chain leading to these extremes.…”

“…Recurrent planetary-scale atmospheric anomalies, such as those associated with planetary wave-patterns and the closely-related storm-track variability, provide an effective lens for interpreting different categories of compound events, from multivariate extremes such as wet and windy episodes (e.g. Messori et al, 2019;De Luca et al, 2020a) to spatially compounding heatwaves (e.g. Kornhuber et al, 2019; to compound long-lasting anomalies (Yiou and Jézéquel, 2020).…”