东亚高空急流协同变化对冬季欧亚遥相关型气候效应的影响

The Influence of Upper Level Jet Streams in East Asia on Climatic Effects of Eurasian Teleconnection Pattern in the Winter

利用NCEP/NCAR再分析资料和我国地面735站气温和降水资料,首先分析了欧亚遥相关型的时间演变和结构特征,在此基础上探讨了欧亚遥相关型不同位相时东亚大气环流的差异,并进一步研究了欧亚遥相关型影响我国冬季气温和降水过程中东亚高空急流的重要作用。从结构上看,欧亚遥相关型位势高度异常中心位于250hP a高度,表现出准正压的结构。欧亚遥相关型位于正位相时,东亚温带急流强度偏弱且位置向北移动;副热带急流强度偏强,两支急流在45°N附近有明显分界;西伯利亚高压和阿留申低压强度增强;东亚大槽加深,槽线倾斜不明显。负位相时则相反。欧亚遥相关型与东亚高空急流的联系是其影响我国气温降水的重要原因。正欧亚遥相关型时,偏弱的温带急流区较强的北风分量有利于北方冷空气南下,从而造成我国气温偏低;偏强的副热带急流区增强的南风将副热带地区暖湿空气向北输送,两支急流协同变化,影响我国冬季降水异常的分布。去掉温带急流或副热带急流偏强的年份,欧亚遥相关型与我国温度、降水的相关性显著减弱,说明欧亚遥相关型是通过东亚高空急流协同变化的桥梁,对我国温度和降水异常产生影响。进一步研究发现,欧亚遥相关型与副热带急流的关系不如其与温带急流稳定,导致在欧亚遥相关型同一位相时东亚高空急流存在两种不同的配置,这种高空急流配置的不唯一性使得东亚高空急流能对欧亚遥相关型的气候效应起到调控作用。

Monthly NCEP/NCAR reanalysis dataset and temperature/precipitation data collected at 735 stations in China are used to investigate variations of Eurasian Teleconnection pattern （EU） and East Asian jet streams （EAJSs）. The EU pattern shows a quasi-barotropic structure with obvious geopotential height anomalies at 250 hPa. In the positive EU phase, the East Asian polar front jet （PFJ） tends to be weakened and shifts northward; the subtropical jet （SJ） intensifies, inducing two well-separated branches. In the meantime, the Siberian High, the Aleutian Low, and the East Asian trough all strengthen. The situations in the negative EU phase are opposite to those in the positive phase. The close relationship between the EU and EAJSs plays an important role in the climatic effect of EU pattern. In positive EU phase, cold air from the high-latitudes moves southward due to strong meridional winds in the PFJ region and the winter temperature in China tends to be colder than normal. The warm air brought by the strong SJ and the cold air brought by the PFJ influence the distribution of precipitation anomalies in China. The concurrent variation of PFJ and SJ is the main mechanism for the EU to influence temperature/precipitation anomalies in China. After removing the years when the PFJ or SJ is strong, the obvious correlation between EU pattern and temperature/precipitation in China disappears. This result indicates that EAJSs can act as a bridge that links the EU signal with the variation of temperature/precipitation in China. Further study finds that the relationship between the EU and PFJ is more stable than that between EU and SJ. The configuration of PFJ and SJ is different even in the same EU phase. The non-unique configuration of EAJSs in the same EU phase provides an opportunity for EAJSs to influence the climatic effects of the EU pattern.