From the Potsdam Institute for Climate Impact Research (PIK)
In the Northern Hemisphere mid-latitudes, much of the day-to-day weather variability is determined by the storm track regions located over the Atlantic and Pacific oceans. Here, weather systems, including storms, are generated and travel eastwards to the continents. In winter, storms bring air from the relatively warm oceans to the continents and thus have a warming effect. In summer, the effect reverses with winds bringing relatively cool and moist air from the sea. The authors show that a lack of such weather systems can thus favor more persistent heat and drought events in summer, and cold spells in winter.
Changes in mid-latitude circulation can strongly affect the number and intensity of extreme weather events. In particular, high-amplitude quasi-stationary planetary waves have been linked to prolonged weather extremes at the surface. In contrast, analyses of fast-traveling synoptic-scale waves and their direct influence on heat and cold extremes are scarce though changes in such waves have been detected and are projected for the 21st century. Here we apply regression analyses of synoptic activity with surface temperature and precipitation in monthly gridded observational data. We show that over large parts of mid-latitude continental regions, summer heat extremes are associated with low storm track activity. In winter, the occurrence of cold spells is related to low storm track activity over parts of eastern North America, Europe, and central- to eastern Asia. Storm tracks thus have a moderating effect on continental temperatures. Pronounced storm track activity favors monthly rainfall extremes throughout the year, whereas dry spells are associated with a lack thereof. Trend analyses reveal significant regional changes in recent decades favoring the occurrence of cold spells in the eastern US, droughts in California and heat extremes over Eurasia.
The influence of mid-latitude storm tracks on hot, cold, dry and wet extremes by Jascha Lehmann and Dim Coumou published in Nature Scientific Reports, DOI 10.1038/srep17491
Read the abstract and get the paper here.
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