2013/2014年东亚冬季风异常偏弱的可能成因

2005年之后东亚冬季风连续7年强度偏强,而2013/2014年冬季,东亚冬季风强度突然由强转弱,原因可能与前期秋季北极海冰的异常有关,受2013年秋季北极海冰异常影响,冬季西伯利亚高压偏弱,进而导致东亚冬季风偏弱以及我国气温偏高。季内,东亚冬季风强度变化显著,前冬偏弱,后冬偏强。受冬季风季节内变化影响,我国前冬暖、后冬冷;此外,前冬暖、后冬冷还受到北太平洋上空阻塞高压的异常活动影响,北太平洋地区的阻塞高压加强西移至日界线以西,导致东亚地区经向型环流加强,改变了前冬以纬向型为主的环流,前冬高纬地区堆积的冷空气向东亚地区侵袭。加之,前冬我国气温偏高,导致后冬我国多地降温显著,气温由偏高转偏低。而阻塞高压的西移可能与平流层环流的异常活动有关。

Possible Causes for the Anomalous Weak East Asian Winter Monsoon in 2013/2014

The East Asian winter monsoon was stronger than normal continuously for seven years since 2005, but it suddenly shifted to be weaker than normal in winter 2013/2014. The research results indicated that the increased Arctic sea ice extent in the last autumn was responsible for the negative sea level pressure in Siberia in winter 2013/2014, resulting in the weakening of Siberian high which was favorable for the anomalous weak East Asian winter monsoon and high temperature in China. During the winter, East Asian winter monsoon exhibited strong intraseasonal variations, weaker in the early winter and stronger in the late winter. Accompanying the intraseasonal variations of the East Asian winter monsoon, the temperature over China had two stage variations in the last winter, warmer in the early winter and colder in the late winter. Furthermore, the warmer in the early winter and colder in the late winter over China also was influenced by the blocking high activities over the North Pacific. In the late winter, the westward shifting of the blocking high to the west of date line strengthened the merional circulation over East Asia, leading the sweeping down of the cold air over East Asia, further causing the anomalous low temperature in China in the late winter. However, the westward shift of the blocking high over the North Pacific may be related to the stratospheric circulation anomalies.