The Independent and Coordinative Influences of the Four Blocking Systems in the Northern Hemisphere Winter on the Occurrence of Widespread Extreme Cold Surface Temperature

Based on 1979-2015 ERA-interim daily reanalysis data, this paper analyzes the independent and coordinative effects of four blocking systems (the Greenland blocking, GB; the Atlantic-Europe blocking, AEB; the Ural blocking, UB; the North Pacific blocking, NPB) on surface air temperature (SAT) and extreme cold days on interannual and synoptic scales. The results show that the statistical relationship between the blocking systems and SAT is very complicated. The same blocking system can affect SAT anomalies in many areas. Meanwhile, the SAT in the same area is generally affected by many blocking systems. By separating a single blocking from multiple blockings (double blockings, three blockings and four blockings), it is further demonstrated that the influence of UB on Eurasia SAT is the most important. However, the blocking systems that have secondary impacts on SAT over Europe and Asia are different. AEB, GB and NPB rank next for Europe while GB, NPB and AEB rank next for Asia in order of importance. The blocking system that has the most important influence on the SAT over the North American is NPB, followed by GB and AEB, and the effect of UB is the weakest. In addition, the coordinative effects of multiple blocking systems on SAT are significantly nonlinear instead of a linear superposition.