Abstract
The effects of rapid Arctic warming and ice loss on weather patterns in the Northern Hemisphere is a topic of active research, lively scientific debate and high societal impact. The emergence of Arctic amplification—the enhanced sensitivity of high-latitude temperature to global warming—in only the last 10–20 years presents a challenge to identifying statistically robust atmospheric responses using observations. Several recent studies have proposed and demonstrated new mechanisms by which the changing Arctic may be affecting weather patterns in mid-latitudes, and these linkages differ fundamentally from tropics/jet-stream interactions through the transfer of wave energy. In this study, new metrics and evidence are presented that suggest disproportionate Arctic warming—and resulting weakening of the poleward temperature gradient—is causing the Northern Hemisphere circulation to assume a more meridional character (i.e. wavier), although not uniformly in space or by season, and that highly amplified jet-stream patterns are occurring more frequently. Further analysis based on self-organizing maps supports this finding. These changes in circulation are expected to lead to persistent weather patterns that are known to cause extreme weather events. As emissions of greenhouse gases continue unabated, therefore, the continued amplification of Arctic warming should favour an increased occurrence of extreme events caused by prolonged weather conditions.
Highlights
A variety of positive feedbacks—processes that amplify an original change—cause the Arctic to be more sensitive2015 The Authors
Amplified jet-stream patterns (HAPs) are responsible for many extreme weather events [15]; an increased frequency of these patterns would be expected to result in an increase in extreme weather events
Because Highly amplified jet-stream patterns (HAPs) have been linked with a variety of extreme weather types [15], our findings suggest that the recent increase in extreme weather events throughout the Northern Hemisphere mid-latitudes [29] may be partly due to the rapid pace of Arctic warming
Summary
A variety of positive feedbacks—processes that amplify an original change—cause the Arctic to be more sensitive. The result of the enhanced ridge/trough couplet is an increase in wave energy, which is transferred into the stratosphere, where it can disrupt the polar vortex and lead to further meandering in the jet stream later in winter The fact that these three independent studies identified the same mechanism using different approaches, data sources and model experiments suggests that the linkage is robust. A primarily summer mechanism proposed and demonstrated by Petoukhov et al [19] and Coumou et al [6] suggests that the weakened poleward gradient owing to AA is conducive to the formation of a split-jet structure during summer months that acts as a waveguide, trapping and amplifying large jet-stream waves These waves become nearly stationary, creating persistent weather conditions that have contributed to an increasing number of temperature and precipitation extremes over Northern Hemisphere continents. Because the atmosphere is inherently chaotic and the signal of AA has emerged only recently, it is a challenge to detect robust changes in the character of the jet stream [22,23] and separate the various influences on its behaviour
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