Teleconnections and Future Changes in the East Asian Winter Monsoon under Arctic Amplification

Description

After the severe and prolonged snowstorms in South China in January 2008, severalextreme cold spells hit different parts of the Northern Hemisphere in the six wintersbetween 2008/09 and 2013/14. Because the intensity and duration of these cold spellswere exceptional in the past few decades, more research should be devoted tounderstanding the underlying physical mechanisms of cold extremes under a changingclimate in order to better predict their occurrence in the future.In East Asia, the occurrence and persistence of extreme cold spells are closely related toan anomalous East Asian winter monsoon. These cold spells are preceded by blockingevents near the Ural Mountains and the western Pacific. The occurrence of blockingevents is linked with low-frequency atmospheric oscillations, such as the North AtlanticOscillation and the El Nino/Southern Oscillation. Estimations of future Ural and westernPacific blocking frequency and characteristics are crucial for projecting change in theEast Asian winter monsoon.Since 1990, a significant winter cooling trend has occurred in the midlatitudes, includingwestern Siberia, where cold air activity in East Asia originates. Simultaneously, apronounced warming trend has been observed over the polar region accompanying thereduction of Arctic sea ice, which is known as the Arctic amplification. Arcticamplification has thus occurred alongside cold midlatitude winters in recent years, incontrast to cold winters in earlier periods. Under a global warming trend, Arcticamplification may exert an impact on the large-scale teleconnections of the East Asianwinter monsoon with blocking in the midlatitudes, but the underlying mechanisms arenot yet fully understood.One area of particular concern is the effect that climate change and the substantialreduction of Arctic sea ice might have on the winter monsoon circulation over East Asia.How the East Asian winter monsoon will respond to a warmer planet is not totally clear.One possibility is that anomalous blocking events (frequency, location, intensity,duration) due to Arctic amplification and sea ice loss may enhance extreme cold spells,but the mechanisms potentially involved in such changes are still under discussion. Forexample, the Hong Kong Observatory recorded 24 consecutive cold days from 24 Januaryto 16 February 2008, which is the longest cold spell since 1968. Due to the huge economicloss this prolonged cold spell caused in South China, it is important to better prepare forthe impact of cold extremes under the global warming trend.