Southward cold airmass flux associated with the East Asian winter monsoon: Diversity and impacts

The wintermonsoon has strong impacts on East Asia via latitude-crossing southward cold airmass fluxes called cold air outbreaks (CAOs). CAOs have a high diversity in terms ofmeridional extent and induced weather. Using the daily cold airmass flux normalized at 50° and 30°N during 1958-2016, we categorize the CAOs into three groups: high-middle (H-M), high-low(H-L), andmiddle-low (M-L) latitude events. The H-L type is found to have the longest duration, and the M-L type is prone to strong CAOs regarding normalized intensity. The H-L and H-M events feature a large-scale dipole pattern of cold airmass flux over high-latitude Eurasia; the former events feature relatively strong anticyclonic circulation over Siberia, while the latter events feature cyclonic circulation over northeastern Asia. In contrast, the M-L events are characterized by a cyclonic anomaly over northeastern Asia but no obvious high-latitude precursor. The H-L events have the greatest cold anomaly in airmasses near the surface, and the M-L events mainly feature a strong northerly wind. As a result, the H-L events induce widespread long-lasting low temperatures over East Asia, while the M-L events induce a sharp temperature drop atmainly low latitudes. Both H-L and M-L events couple with the MJO to enhance rainfall over the South China Sea, while H-M events increase rainfall over southern China. Moreover, the occurrences of H-L and M-L events have experienced a long-term decrease since the 1980s that has induced a stronger warming trend in the cold extremes than in the winter mean temperature at mid-low latitudes over East Asia.