Recent enhanced high-summer North Atlantic Jet variability emerges from three-century context

V Trouet,F Babst,M Meko

doi:10.1038/s41467-017-02699-3

Abstract

A recent increase in mid-latitude extreme weather events has been linked to Northern Hemisphere polar jet stream anomalies. To put recent trends in a historical perspective, long-term records of jet stream variability are needed. Here we combine two tree-ring records from the British Isles and the northeastern Mediterranean to reconstruct variability in the latitudinal position of the high-summer North Atlantic Jet (NAJ) back to 1725 CE. We find that northward NAJ anomalies have resulted in heatwaves and droughts in northwestern Europe and southward anomalies have promoted wildfires in southeastern Europe. We further find an unprecedented increase in NAJ variance since the 1960s, which co-occurs with enhanced late twentieth century variance in the Central and North Pacific Basin. Our results suggest increased late twentieth century interannual meridional jet stream variability and support more sinuous jet stream patterns and quasi-resonant amplification as potential dynamic pathways for Arctic warming to influence mid-latitude weather.

Highlights

A recent increase in mid-latitude extreme weather events has been linked to Northern Hemisphere polar jet stream anomalies
The two well-replicated (Fig. 2d) temperature proxies explain 52% (r = 0.72, p < 0.001; 1901–1978; Fig. 2a) and 44% (r = 0.66, p < 0.001; 1901–1980; Fig. 2b) of the variance in regional August average temperature variation in British Isles (BRIT) and northeastern Mediterranean (NEMED), respectively, and illustrate the temperature dipole generated by anomalous North Atlantic Jet (NAJ) positions
Enhanced late twentieth century variance has been detected in climate and ecosystem dynamics in the Central[31] and Northeast Pacific[32,33] (Fig. 5d–f)

Summary

Introduction

A recent increase in mid-latitude extreme weather events has been linked to Northern Hemisphere polar jet stream anomalies. One hypothesis suggests variability in the amplitude and speed of the Northern Hemisphere jet stream as a potential mechanism linking recent midlatitude weather extremes to anthropogenic warming[16,17,18] This hypothesis is largely based on statistical associations between observational or atmospheric reanalysis data that are supported by plausible physical mechanisms. Our NAJ reconstruction shows that late twentieth century NAJ positions fall within the range of the preceding centuries, but that a recent increase in the number of NAJ anomalies is unprecedented This increase in NAJ variance coincides with enhanced variance in the Pacific Basin and points to an increase in interannual meridional jet stream variability since the 1960s

Methods

Results

Conclusion