The New Definition Of Polar/Eurasian Teleconnection Type And Its Weather Impact In May

The Polar/Eurasia(POL)pattern was previously identified based on the empirical orthogonal function method and monthly mean data,in which the positive and negative phases are anti-symmetric in spatial distribution.This paper identifies the positive(POL~+)and negative(POL?)phases of the POL pattern through applying a novel approach,i.e.,self-organizing maps,to daily 500 hPa geopotential height fields in May over 1948-2017.The POL~+and POL?patterns defined in this method represent actual physical modes.The POL~+pattern features a wave train from the northeastern Atlantic/northern Europe via the subarctic regions of Eurasia to Lake Baikal.The POL?pattern is not anti-symmetrical with the positive phase and is characterized by a planetary-scale dipole pattern with a positive anomaly band over subarctic Eurasia and a negative anomaly band in mid-latitude from central Asia to the Sea of Okhotsk.The POL~+pattern occurred frequently in the 1960s and during mid-1980s to mid-2000s.The POL?pattern occurred mostly in the 1950s and 1970s.The weather effects of POL~+and POL?patterns on Eurasia are different.The POL~+pattern increases the blocking frequency over the northeastern Atlantic/northern Europe and northeastern Asia,where high-frequency transient eddies are highly recurrent in the north.Accordingly,precipitation increases apparently in the subarctic Asian continent and western Siberia and decreases around Europe and Lake Baikal.A mimic wave train is also observed in the surface air temperature anomalies field,A remarkable temperature increase occurs in northeastern Asia,while a significant temperature decrease is observed around the Ural Mountains.During the POL?period,the blocking frequency is abnormally high over mid-latitude Eurasia,whereas high-frequency transient eddies are apparently suppressed over northern Eurasia.Correspondingly,significant precipitation deficits are observed in northern Eurasia.The POL?pattern also causes a remarkable temperature increase in the subarctic seas of Eurasia and a considerable temperature drop in the mid-latitude Asian continent.The POL?pattern has a more prominent impact on the temperature and precipitation weather in China.According to the e-fold time scale,we divides the intra-seasonal evolution of the May POL?pattern event into three types,namely,perturbation type(SL),move type(ML)and continuous type(LL),which duration increases in turn,and the formation and maintenance mechanism of different POL?pattern are discussed from two aspects:Rossby wave energy dispersion and transient eddy feedback forcing.The Rossby wave energy dispersion process from the upstream is the main factor in their formation,development and maintenance,but the origin of the Rossby wave is different.The SL type originates from the North Atlantic region,and the ML type and LL type wave train originate from the upper reaches.The Labrador Peninsula region of North America,but the LL type Rossby wave energy transmission is stronger and earlier.Local transient forcing has a direct contribution to the overall evolution of the SL type.transient forcing is conducive to the formation and development of the ML type,but not conducive to the maintenance of the positive anomaly region in the Eurasian subpolar region.For the LL type,transient forcing The effect is obvious after the beginning of the peak period.