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Amplified mid-latitude planetary waves favour particular regional weather extremes

2014; Nature Portfolio; Volume: 4; Issue: 8 Linguagem: Inglês

10.1038/nclimate2271

1758-6798

James A. Screen, Ian Simmonds,

Atmospheric aerosols and clouds

An increase in extreme weather events in the Northern Hemisphere mid-latitudes has been proposed as a result of amplification of atmospheric planetary waves in the region. This study finds months of extreme weather are associated with amplified planetary waves, with different types of extreme events associated to differing degrees. There has been an ostensibly large number of extreme weather events in the Northern Hemisphere mid-latitudes during the past decade1. An open question that is critically important for scientists and policy makers is whether any such increase in weather extremes is natural or anthropogenic in origin2,3,4,5,6,7,8,9,10,11,12,13. One mechanism proposed to explain the increased frequency of extreme weather events is the amplification of mid-latitude atmospheric planetary waves14,15,16,17. Disproportionately large warming in the northern polar regions compared with mid-latitudes—and associated weakening of the north–south temperature gradient—may favour larger amplitude planetary waves14,15,16,17, although observational evidence for this remains inconclusive18,19,20,21. A better understanding of the role of planetary waves in causing mid-latitude weather extremes is essential for assessing the potential environmental and socio-economic impacts of future planetary wave changes. Here we show that months of extreme weather over mid-latitudes are commonly accompanied by significantly amplified quasi-stationary mid-tropospheric planetary waves. Conversely, months of near-average weather over mid-latitudes are often accompanied by significantly attenuated waves. Depending on geographical region, certain types of extreme weather (for example, hot, cold, wet, dry) are more strongly related to wave amplitude changes than others. The findings suggest that amplification of quasi-stationary waves preferentially increases the probabilities of heat waves in western North America and central Asia, cold outbreaks in eastern North America, droughts in central North America, Europe and central Asia, and wet spells in western Asia.