Comparison of Persistent Cold Events in China during January–February of 2018 and 2008

A persistent cold event affected China through late January to early February 2018, causing severe damage to the life and property of the country. The event exhibits a resemblance to the well-known long-lasting snowstorms of January 2008 (“0801” event in brief), because both the events occurred during the La Niña phase along with reduced sea ice in the Arctic during the preceding autumn. In this study, the observational features of the 2018 event and the possible factors for its occurrence are investigated through a comparison with the “0801” event. The 2018 cold event persisted for a relatively shorter period than the “0801” event, with cold air outbreak along with an eastern pathway rather than a northwestern or northern pathway, as was seen in “0801”. Large-scale atmospheric circulation exhibited a substantial difference between the two cases. The Ural blocking and the East Asian grand trough, the two key systems consisting of East Asian winter monsoon (EAWM), which formed a “west-high-east-low” pattern, were significantly stronger in the 2018 event. In comparison, the East Asian grand trough in the “0801” event did not deepen as evidently, despite the similarly enhanced Ural blocking. Instead, a substantially deepened southern branch trough, another important composition of EAWM, developed in “0801” and resulted in a “north-high-south-low” pattern. Also, the Siberian high persisted for a shorter period in the 2018 event. Besides, tropical convection activities exhibited difference between the two cases. Enhanced convection occurred in the Maritime Continent and equatorial western Pacific in the 2018 case, but mainly over the equatorial Indian Ocean during the “0801” event. The latter contributed to the strengthening of the southern branch trough and the western Pacific subtropical high leading to intensified water vapor transportation from the Bay of Bengal and the western Pacific, and intensified precipitation. In comparison, the convection in 2018 was substantially weaker and not so favorable for transporting moisture to South China.