Quasi-stationary extratropical wave trains associated with distinct tropical Pacific seasonal mean convection patterns: observational and AMIP model results
In this paper, mechanisms for the formation of quasi-stationary extratropical wave trains associated with four distinct winter patterns of seasonal mean tropical Pacific convection anomalies, including the western CP (W-CP) pattern, La Niña (LN) pattern, CP El Niño (CPEN) pattern and EP El Niño (EPEN) pattern, are investigated by utilizing observational and six Atmospheric Model Intercomparison Project Phase 5 (AMIP5) high-skilled models (ACCESS1.0, CanAM4, CCSM4, CMCC-CM, HadGEM2-A, MPI-ESM-LR) datasets. The observational results show that tropical Pacific forcing induces upper-level anomalous Rossby wave source that force vorticity over the central North Pacific through modulating the local Hadley circulation, then excite eastward propagation of quasi-stationary planetary waves penetrating into the North Atlantic, and finally establish the associated teleconnections in mid- and high-latitudes by local synoptic eddy–mean flow interaction. Different structures of wave trains may be explained by evident differences in intensity and scale of the extratropical vorticity forcing originating from distinct convection anomalies over the tropical Pacific. The MME results further confirm the possible physical processes obtained from observations, but there still exist some significant differences. These cover the North Pacific and North America and can possibly be attributed to the models’ simulation ability of extratropical vorticity forcing and local storm track intensity. In addition, the stratosphere–troposphere interaction plays an important role for extratropical atmospheric circulation anomalies. The stratospheric polar vortex not only modulates the underlying wave train, especially for the North Atlantic/Europe sector, but is also affected by the upper-tropospheric disturbance in high-latitudes through the upward wave activity flux.
KeywordsTropical Pacific convection Extratropical wave train Synoptic eddy–mean flow interaction Extratropical vorticity forcing Storm track
We thank the two anonymous reviewers for their valuable comments and suggestions, which led to significant improvement in the manuscript. This study is supported jointly by the National Key Research and Development Program of China (Grant No. 2016YFA0600604), the National Natural Science Foundation of China (Grants 41705051 and 41721004), the Chinese Academy of Sciences Key Research Program of Frontier Sciences (QYZDY-SSW-DQC024), and the Jiangsu Collaborative Innovation Center for Climate Change.
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Conflict of interest
The authors declare that they have no conflict of interest.
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