Cold season Africa–Asia multidecadal teleconnection pattern and its relation to the Atlantic multidecadal variability
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A prominent teleconnection pattern of multidecadal variability of cold season (November to April) upper-level atmospheric circulation over North Africa and Eurasia (NA–EA) is revealed by empirical orthogonal function analysis of the Twentieth Century Reanalysis data. This teleconnection pattern is characterized by an eastward propagating wave train with a zonal wavenumber of 5–6 between 20° and 40°N, extending from the northwest coast of Africa to East Asia, and thus is referred to as the Africa–Asia multidecadal teleconnection pattern (AAMT). One-point correlation maps show that the teleconnectivity of AAMT is strong and further demonstrate the existence of the AAMT. The AAMT shapes the spatial structure of multidecadal change in atmospheric circulation over the NA–EA region, and in particular the AAMT pattern and associated fields show similar structures to the change occurring around the early 1960s. A strong in-phase relationship is observed between the AAMT and Atlantic multidecadal variability (AMV) and this connection is mainly due to Rossby wave dynamics. Barotropic modeling results suggest that the upper-level Rossby wave source generated by the AMV can excite the AAMT wave train, and Rossby wave ray tracing analysis further highlights the role of the Asian jet stream in guiding the wave train to East Asia. The AAMT acts as an atmospheric bridge conveying the influence of AMV onto the downstream multidecadal climate variability. The AMV is closely related to the coordinated change in surface and tropospheric air temperatures over Northwest Africa, the Arabian Peninsula and Central China, which may result from the adiabatic expansion/compression of air associated with the AAMT.
KeywordsAtlantic multidecadal variability Africa–Asia multidecadal teleconnection pattern Rossby wave train Africa–Asia multidecadal climate variability
The authors wish to thank the anonymous reviewers for their constructive comments that significantly improved the quality of this paper. This work was jointly supported by the National Key Research and Development Plan (2016YFA0601801), the National Science Foundation of China (41290255 and 41405128), and the National Programme on Global Change and Air-Sea Interaction (GASI-IPOVAI-06 and GASI-IPOVAI-03).
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