Weakened potential vorticity barrier linked to recent winter Arctic sea-ice loss and mid-latitude cold extremes

AbstractA winter Eurasian cooling trend and a large decline of winter sea ice concentration (SIC) in the Barents-Kara Seas (BKS) are striking features of recent climate changes. The question arises as to what extent these phenomena are related. In this paper a mechanism is presented that establishes a link between recent winter SIC decline and midlatitude cold extremes. Such potential weather linkages are mediated by whether there is a weak north-south gradient of background tropospheric potential vorticity (PV). A strong background PV gradient, which usually occurs in North Atlantic and Pacific midlatitudes, acts as a barrier that inhibits atmospheric blocking and southward cold air intrusion. Conversely, atmospheric blocking is more persistent in weakened PV gradient regions over Eurasia, Greenland, and northwestern North America due to weakened energy dispersion and intensified nonlinearity.The small climatological PV gradients over mid-high latitude Eurasia have become weaker in recent decades as BKS ...