Three Eurasian teleconnection patterns: spatial structures, temporal variability, and associated winter climate anomalies
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The Eurasian (EU) pattern is a distinct teleconnection pattern observed in boreal winter. Since the EU pattern was first identified, three types have been reported in the literature: the conventional EU pattern; the type 1 EU pattern, or Scandinavian (SCAND) pattern; and the type 2 EU pattern, or East Atlantic/West Russia (EATL/WRUS) pattern. Based on several reanalysis and observational datasets, the three EU patterns are extracted using the rotated empirical orthogonal function method. In order to provide a further distinction and understanding of the three EU patterns, a comprehensive side-by-side comparison is performed among them including their temporal variability, horizontal and vertical structure, related stationary Rossby wave activity, impact on climate, and possible driving factors associated with external forcing. The results reveal that all three EU patterns are characterised by a clear quasi-barotropic wave-train structure, but each has a distinct source and centre of action. Accordingly, their impacts on the precipitation and surface air temperature also differ from one other. Further evidence suggests that the conventional EU pattern is likely driven by anomalous sea surface temperatures (SST) over the North Atlantic, in which process the transient eddies are actively involved. The SCAND pattern is partly maintained by the vorticity source over Western Europe, which arises from the anomalous convergence/divergence over the Mediterranean and is efficiently driven by the tropical and southern Indian Ocean SST via divergent circulation. The EATL/WRUS pattern shows some linkage to the North American snow cover, and the involved process remains unclear and needs further investigation.
KeywordsEurasian pattern Scandinavian pattern East Atlantic/West Russia pattern REOF Rossby wave activity
We thank the three reviewers for their constructive comments and suggestions that led to significant improvement of the manuscript. Discussions with Profs. H Nakamura, RG Wu, and Drs. PD Sardeshmukh, GS Chen, ZD Lin, and K Nishii are appreciated. This work was supported by the National Natural Science Foundation of China (41230527, 41025017), the China Special Fund for Meteorological Research in the Public Interest (GYHY201406018), the Research Grants Council of the Hong Kong Special Administrative Region (104410), and the City University of Hong Kong Strategic Research Program (7002917).
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