Anti-Phase Variations of Atmospheric Mass between Eurasian Continent and North Pacific and the Related Boreal Winter Climate Anomalies over Eurasia

Abstract:

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. An index is defined for describing this MAMLO phenomenon. Our results have demonstrated that there is an anti-phase relationship in anomalous AM variations over regions between Eurasia and mid-latitude North Pacific, which is referred to as Eurasia-(North)Pacific anti-phase relation (EPAR). This EPAR 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 EPAR teleconnection is significantly associated with three factors including the anomalous AM flows, 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 are closely related to MAMLO phenomenon. When the MAMLO 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 Eurasia in the mid- and high- latitudes and East Asia, whereas increases (decreases) over regions of the Mediterranean, 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.