中文摘要：

利用1961-2000年NCEP/NCAR月平均再分析资料对东亚副热带西风急流强度和位置的季节变化进行了分析,指出急流位置季节变化不仅有明显的南北向移动,6-7月还存在东西方向的突变特征,同时急流轴在北进过程中具有东西向的不一致性,急流中心强度的变化超前于位置的南北移动.在此基础上,采用动态追随急流中心移动的方法,探讨东亚副热带西风急流季节变化的热力影响机制,发现东亚副热带西风急流强度变化及位置移动与对流层中上层气温南北差异的分布结构有很好的对应关系,这说明急流的季节演变是对辐射季节变化及由于东亚特殊的海陆分布和青藏高原大地形影响而造成纬向不均匀加热的响应.从各热量输送项与急流的关系来看,从冬半年到夏半年的增暖时段,急流中心南北温差减小,急流减弱北进;从夏半年到冬半年的降温时段,急流中心南北温差增大,急流加强南退.热量平流输送的经向差异是造成急流中心南北温差的主要原因,急流跟随热量平流输送最大经向梯度中心位置南北移动.非绝热加热对急流中心的东西移动有引导作用,青藏高原春夏季对对流层中上层强大的加热作用是导致6-7月急流中心位置西移突变的原因.

英文摘要：

The seasonal variations of the intensity and location of the East Asian subtropical Westerly Jet （EAWJ） and its thermal mechanism are analyzed by using the NCEP/NCAR monthly reanalysis data from 1961 to 2000. It is found that the seasonal variation of the EAWJ core not only has significantly meridional migration, but also shows the rapid latitudinal displacement during June-July. Moreover, there exists the zonal inconsistency in the northward shift process of the EAWJ axis, and the change in the jet intensity usually occurs before the meridional shift of the EAWJ. The thermal mechanism of the seasonal variation of EAWJ is also examined by tracking the core of the EAWJ. The results indicate that the annual cycle of the EAWJ matches very well with the structure of the meridional temperature differences in the upper and middle troposphere, suggesting that the seasonal variation is the response of EAWJ to the seasonal variation of solar radiation, and the thermal contrast of land/ sea and the megarelief of the Tibetan Plateau. Through investigating the relation between the EAWJ and heat transports, it is found that the EAWJ weakens and shifts northwards during the warming period from winter- time to summertime, whereas the EAWJ intensifies and shifts southward during the cooling period from summertime to wintertime. The meridional difference of heat advection transport is the domonant factor determining the meridional temperature difference around the EAWJ center, and the south-north shift of the EAWJ follows the maximum meridional gradient of the heat advection transport. During the period from April to October the diabatic heating plays a leading role in the longitudinal displacement of the EAWJ center, and the strong diabatic heating of the Tibetan Plateau in the mid-upper troposphere leads to the rapid longitudinal displacement of the EAWJ center in early summer during June to July.