2011～2012年冬季欧亚大陆低温严寒事件与平流层北极涛动异常下传的影响

Strong Cold Weather Event over Eurasia during the Winter of 2011/2012 and a Downward Arctic Oscillation Signal from the Stratosphere

利用NCEP-NCAR再分析资料分析了2011～2012年冬季发生在欧亚大陆的一次异常低温严寒事件的大气环流演变过程以及可能的成因。这次低温事件,主要出现在2012年1月下旬至2月上旬,持续大约3周左右,非常强的低温异常覆盖了几乎整个欧洲以及东亚的西伯利亚、蒙古国和我国东北、华北等地。这次低温事件的演变与对流层北极涛动(AO)由正位相转变为负位相的时间相匹配,意味着AO可能发挥重要作用。进一步分析表明,前期行星波的异常上传导致平流层发生爆发性增温现象,极夜急流减弱,AO位相首先在平流层由正变负;在2～3周左右的时间内,平流层AO异常信号逐渐下传,使得对流层AO也转为负位相;随后,乌拉尔山阻塞高压异常发展,极区的冷空气不断向南爆发,先后在东亚和欧洲造成剧烈的降温,导致低温严寒事件。因此,考虑平流层环流的异常可能有助于提高欧亚大陆冬季低温严寒事件的预测能力。

The circulation evolution and possible causes of a severe cold event over the Eurasian continent during the winter of 2011/2012 were investigated with the NCEP-NCAR reanalysis data. Strong cold anomalies covering most of Europe, Mongolia, and northeastern China began in late January 2012 and lasted for about 3 weeks. Analysis results indicate that this cold event coincided with the phase of the Arctic Oscillation （AO） changing from positive to negative, which implied a possible impact of the AO. Before this AO phase change, a minor warming occurred in the stratosphere caused by an anomalous upward propagation of planetary waves. The polar night jet then decelerated and the AO changed its sign in the stratosphere. Within 2-3 weeks, the stratospheric AO signal gradually propagated downward and accordingly the tropospheric AO evolved into the negative phase. Thus, a strong Ural blocking high developed, and cold air invaded Europe and East Asia from the polar region, which induced the decreasing temperature there. Our results suggest that improvements can be made in predicting severe winter cold events over Eurasia by taking into account the stratospheric circulation anomaly.