Precursory signals of East Asian winter cold anomalies in stratospheric planetary wave pattern
The impacts of the stratospheric polar vortex changes on the tropospheric climate variability have been emphasized in previous studies. The present study presents evidence for precursory signals of cold anomalies over East Asia in the stratospheric wave pattern during November through March. The leading two empirical orthogonal function (EOF) modes of daily 50-hPa geopotential height anomalies along 65°N correspond to changes in the amplitude and phase of the stratospheric planetary wavenumber 1, respectively. Composite analysis is performed to unravel the temporal evolution of anomalies during 8 phases of 34 events identified based on the second EOF mode with a complete life cycle for the period 1979–2016. The surface cold anomalies over eastern China emerge in phase 3 (corresponding to negative and positive 50-hPa height anomalies on the North Atlantic and Russian Far East sector, respectively) and peak in phase 5 (corresponding to positive 50-hPa height anomalies over Eurasia) when the Siberian high extends southeastward and the East Asian trough deepens with anomalous surface northerly winds. Downward propagation of stratospheric signal is detected over western Europe and western Siberia. The former is a source region of the tropospheric Rossby wave trains propagating along the polar front jet and subtropical jet. The downward propagation of stratospheric signal is related to the reflection of stratospheric planetary wavenumber 1 pattern and contributes to the development of the tropospheric Rossby wave train that, in turn, leads to the strengthening of the Siberian high and the deepening of the East Asian trough.
KeywordsEast Asian cold anomalies Precursory signals Stratospheric planetary wave pattern Downward propagation
This study is supported by the National Natural Science Foundation of China grants (41705063, 41530425, 41475081, 41661144016, 41775080, and 41275081). The NCEP reanalysis 2 data were obtained from ftp://ftp.cdc.noaa.gov/.
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