2007／2008年冬季平流层环流异常及平流层-对流层耦合特征

Stratospheric Oscillation and Stratosphere-Troposphere Coupling in 2007/2008 Winter

利用NCEP／NCAR再分析资料，分析了2007／2008年冬季平流层环流振荡的过程和异常特征，以及平流层—对流层的环流耦合特征。结果发现：2007／2008年冬季平流层极涡持续偏强，且极涡从12月下旬开始向东亚—大西洋地区偏心发展，同时在欧洲—地中海地区减弱向极区收缩，从而在欧亚地区的平流层高层最早形成“一脊一槽”1波型的环流形势；该平流层的环流异常信号逐步向低层传播；从平流层10hPa向下传播到对流层中、低层需要约15～20天的时间；此时对流层500hPa上，与平流层向下传播的信号相对应，呈现为高纬度“西高东低”和副热带“东高西低”的环流异常型，即分别对应着乌拉尔山阻塞高压、鄂霍茨克海低槽以及副热带高压异常偏强和副热带欧亚大陆中西部低槽活动频繁。这种环流异常配置即形成了有利于我国南方降雪持续的大尺度背景条件。进一步研究还发现，平流层异常信号存在由热带向极传播的趋势。2008年1月的平流层极涡振荡正异常所对应的环流异常信号可以追溯到2007年秋季10月份最早出现在热带地区的环流异常信号，该异常信号在向极传播过程中同时向东移动，2008年1月传播到极区，对应极涡振荡的正异常。说明前期平流层的异常信号及其演变，对2008年1月的气候异常具有重要指示意义。

Based on the NCEP/NCAR reanalysis data, the features of the stratospheric oscillations and the stratosphere-troposphere coupling in 2007/2008 winter were analyzed, it was found that the stratospheric polar vortex was persistently stronger during this winter. It was elongated and eccentrically developed along Eastern Asia and Atlantic, and shrank along Western-Euro and Mediterranean since the early December, 2007. Consequently, the ＂one ridge and one trough＂ pattern first appeared in the high stratosphere in the eastern hemisphere. These anomalous stratospheric signals were then propagated systematically downward; it took about 15 -20 days for them to advance from 10 hPa to lower tropospheric levels. Following the propagated signals from upper levels, the corresponding ＂high-in-west and low-in-east＂ pattern in the high latitude, and ＂high-in-east and low-in-west＂ pattern in the subtropics at 500 hPa were clearly seen. They are closely related with the anomalous centers, such as the Siberia blocking high, Okhotsk low, Western-Pacific-Subtropical-High and lows in the mid-western part of Euro-Asia continent, which together favored the formation of sever snow in the south China. Further investigations indicated that there also existed poleward propagations of the stratospheric circulation anomalies that were found generated in the deep tropics. The stratospheric circulation anomalies responsible to the occurrence of the stratospheric polar vortex oscillations in January of 2008 could be tracked back to as early as the middle October in 2007. Accompanying the poleward propagation, the stratospheric anomaly signals were seen moving eastward simultaneously. In all, results from this work are strongly suggesting that our potential ability in predicting the climatic tendency in the troposphere could be significantly improved by catching with the leading stratospheric signals effectively.