北大西洋涛动对新疆夏季降水异常的影响

利用1961~2003年NCEP/NCAR再分析和新疆75个气象站月降水资料，分析新疆夏季降水与沿西亚副热带西风急流Rossby波和北大西洋涛动（NAO）的关系，研究表明，夏季斯堪的纳维亚半岛-中欧—西亚和中亚的准静止波传播是联系NAO与沿西亚副热带西风急流波活动和新疆夏季降水变化的纽带。通过波作用量的动力学诊断分析，讨论了夏季NAO正、负位相异常年准静止波传播特征和差异，夏季NAO强弱活动影响斯堪的纳维亚半岛EP通量散度强度和位置异常，该区EP通量散度强度和位置异常导致强辐散中心在中高纬向东传播的准静止波和沿副热带西风急流准静止波活动变化，从而影响新疆夏季降水。

Effects of the North Atlantic Oscillation on the Summer Rainfall Anomalies in Xinjiang

The relationships between summer rainfall in Xinjiang and Rossby wave activity(RWA) along West Asia subtropical westerly jet stream(WASWJS) and the North Atlantic Oscillation(NAO) are examined by using the NCEP/NCAR reanalysis dataset and 75 stations monthly precipitation data in Xinjiang from 1961 to 2003.The results show that Rossby wave train along Scandinavian Peninsula-middle Europe-WASWJS in summer connects NAO and RWA along WASWJS and summer rainfall variations in Xinjiang.Based on Eliasson-Palm flux(EPF) diagnoses,the characteristics and difference of stationary waves propagation in positive/negative NAO phase years are discussed.Not only does summer NAO impact current regions climate,but also WASWJS and Xinjiang climate in its lower areas.It is found that the strong divergence center of EPF over Scandinavian Peninsula is more westward(eastward) and stronger(weaker) than normal in positive(negative) NAO phase years.There are two horizontal wave activity propagation paths from the strong EPF divergence center over Scandinavian Peninsula in positive NAO phase years.First,the quasi-stationary wave from the EPF divergence center propagates eastward,turns southeastward near the Ural Mountains,enters subtropical westerly jet stream over the Caspian Seap-the Aral Sea,and continues propagating eastward,this wave propagation is stronger than normal.Second,the quasi-stationary wave from the strong EPF divergence center directly propagates southeastward and enters subtropical westerly jet stream near eastern Mediterranean-the Black Sea,so this quasi-stationary wave propagation along WASWJS is stronger than normal in positive NAO phase years.While in negative NAO phase years the quasi-stationary wave from the strong EPF divergence center propagates eastward in high latitude areas,and the quasi-stationary wave from the second strong EPF divergence center propagates southeastward and enters WASWJS near eastern Mediterranean-the Black Sea,the quasi-stationary wave propagation along WASWJS is weaker than normal.As a result,summer NAO activity anomalies cause EPF divergence intensification and position variations over Scandinavian Peninsula,and variations of wave eastward propagation in mid-high latitudes and the quasi-stationary wave activity along WASWJS are induced by these divergence variations,so summer rainfall anomalies in Xinjiang are affected.