Precursory atmospheric circulations with Rossby wave trains leading to Eurasian extreme cold events

Abstract

This work examines precursory atmospheric circulations with various wave trains contributing to extreme cooling over central Eurasia in boreal winter from 1979-2016 based on the ERA-Interim dataset. The empirical orthogonal function (EOF) method is used to classify the anomalous sea level pressure field averaged in two weeks prior to extreme cooling. Based on the classification, three types of precursory atmospheric circulation patterns are named according to the origins of wave trains, and their formation mechanisms are revealed as well . Type1: Baffin Bay-origin pattern, which forms in the downstream development of Rossby wave packets generated from the downward stratospheric energy transmission over the Baffin Bay. Type2: Pacific-origin pattern, similar to a Eurasian (EU) teleconnection pattern, arises at the exit area of the westerly jet in the central North Pacific where cyclonic shear exists; then it develops along the northerly westerly jet over the North Atlantic, which may act as a waveguide to the Eurasian continent. Type 3: Atlantic-origin, manifests as the negative phase of type 2, consistent with the Scandinavian (SCAND) pattern, which may results from the air-sea interaction induced by the warm anomaly of sea surface temperature in the middle of North Atlantic. In conclusion, the three types of precursory atmospheric wave train patterns that bring extreme cooling to Eurasia possess diverse disturbing sources and development mechanisms. The results, which are investigated based on a quasi-biweekly time scale , deepen our understanding of the atmospheric genesis of extreme weather and have specific indicative significance to improve the technique of extended forecast.