In the recent two decades, the impact of Arctic warming on midlatitude atmospheric circulation and cold extremes has become an important research topic because of accelerated Arctic warming.

Winter Ural blocking (UB) is considered to play an important role in winter Eurasian cooling, because it transports cold air from high to middle latitudes and thus affects weather and climate over Eurasia. However, it is unclear what physical processes dominate the influence of the Arctic warming in Barents-Kara seas (BKS) on the UB.

Recently, Prof. LUO Dehai and his Ph.D. student CHEN Xiaodan from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences, along with their collaborators, revealed the physical process of how the winter warming in the Barents-Kara Seas (BKS) changed the duration of the UB events, and established their linkage by inducing a key physical quantity: Meridional potential vorticity (PV) gradient.

Through his nonlinear multi-scale interaction model, Prof. LUO found that the nonlinear behavior of the blocking system was closely related to changes in the energy dispersion and nonlinearity strength. The energy dispersion was proportional to meridional PV gradient, whereas the nonlinearity strength was inversely proportional to the PV gradient.

When the meridional PV gradient was small, the blocking was weakly dispersive and had a strong nonlinearity. In this case, blocking could maintain itself for longer lifetime and had large amplitude. In contrast, the large PV meridional gradient led to the blocking system having strong dispersion and weak nonlinearity. Thus, the blocking was short-lived.

"The meridional PV gradient becomes different under Arctic warming background. The Arctic warming tends to produce a trend toward the PV homogenization with a small PV gradient over Eurasia. As a result, the energy dispersion is weak and the nonlinearity is strong so that the UB does not readily disperse its energy and hence can maintain its long lifetime," said LUO.

These results provide new perspectives of how the mid-latitude atmospheric circulations such as blocking are linked to Arctic warming associated with sea-ice loss.

Schematic diagram of the Arctic warming in BKS affecting the lifetime of UB, where the M-latitude (H-latitude) denotes the middle (high) latitude region, and the PV gradient represents PV meridional gradient. (Image by LUO Dehai)