Associations of atmospheric teleconnections with wintertime extratropical cyclones over East Asia and Northwest Pacific

Extratropical cyclones (ETCs) over East Asia and Northwest Pacific are identified and tracked by applying an objective algorithm to the 850-hPa relative vorticity fields from the ERA-Interim reanalysis. A total of 2866 ETCs originating at the western side of the date line have been identified in the extended November-March winters from 1979 to 2018. The ETC tracks are counted and visualized using a hexagonal tessellation rather than the regular longitude-latitude grids. Two generalized linear models (GLMs), Poisson regression model and Gamma regression model, are firstly applied to investigate the associations of wintertime ETCs with three atmospheric teleconnection patterns. The West Pacific (WP) pattern and the Pacific/North American (PNA) pattern are more responsible for the meridional variability of ETC activities in the North Pacific, while the influence of the Polar/Eurasia pattern on ETC activities is negligible. Results of composite analysis are qualitatively consistent with that of regression analysis. Composite maps of differences of jet stream, thermal gradient and mid-tropospheric baroclinicity in the positive and negative phases of teleconnection patterns also support the close associations of ETC activities with WP and PNA teleconnection patterns.

Automated summary

Extratropical cyclones over East Asia and Northwest Pacific were identified and tracked using an objective algorithm applied to ERA-Interim reanalysis data. The study found that ETC activities are mainly influenced by the West Pacific (WP) and Pacific/North American (PNA) patterns, with negligible impact from the Polar/Eurasia pattern. Composite analysis results supported the close associations of ETC activities with WP and PNA teleconnection patterns.