Eurasia-North Pacific Oscillation in Atmospheric Mass Variations Independent of AO and Its Links to Winter Climate Anomalies

Using NCEP/NCAR reanalysis, we have investigated the features of migrations of atmospheric mass (AM) between Land and Ocean (MAMLO) for Eurasia-North Pacific region in boreal winter. By removing the AO signal out from physical quantities, an index is defined for describing this MAMLO phenomenon. Our results have demonstrated that there exists a teleconnection pattern as Eurasia-North Pacific Oscillation (ENPO) independent of AO. This ENPO pattern characterizes with two major centers of surface air pressure anomalies (SAPA) over those two regions respectively, and varies on timescales ranging from (inter)decadal to inter-annual. The formation of this ENPO teleconnection is significantly associated with three factors including the anomalous AM flows and zonal circulation cell over Eurasia-North Pacific domain, the Rossby wave energy propagations, and the thermal forcing contrasts between Eurasia and North Pacific during boreal winter. The variations of both wintertime rainfall and temperature over Eurasia may be strongly affected by ENPO. When the ENPO index is positive (negative), there occurs the AM accumulation (depletion) over Eurasia with simultaneous depletion (accumulation) over mid-latitude North-Pacific. Correspondingly, this SAPA pattern along with the related circulation anomalies at different isobaric levels possibly results in winter precipitation decreases (increases) over Siberian Plain and East China, whereas increases (decreases) over southeastern Europe, Xinjiang of China, and the west coast of Sea of Okhotsk. On the other hand, surface air temperature decreases (increases) over large areas of Eurasia. These results are helpful for our better understanding the mechanisms behind circulation and winter climate variations over Eurasia-North Pacific region.