北半球中高纬度大气低频变化的若干基本特征

SOME ASPECTS OF LOW FREQUENCY PERTURBATION AT NORTHERN EXTRATROPICS

根据1984～1986年 ECMWF/WMO 客观分析资料的分析结果,揭示了中高纬度大气低频变化的若干特征。结果表明,中高纬度低频扰动的相当正压结构可以用低频扰动的"结构参数"(低频正压动能与低频总动能之比)来表征;中高纬度低频动能的高值区与西风急流的纬向非对称性和经向切变紧密相关;中高纬度低频振荡的传播具有显著的地域性和汇合、分离特征,并可利用中太平洋地区低频反气旋和低频气旋的涡旋对(β-Gyres)的逆时针打转来解释;东亚西风急流入口区所在经度是中低纬度和南北半球低频变化相互作用的关键区域;中高纬度低频涡旋活动与阻塞形势的变化紧密相关。

This study is devoted to some aspects of mid-and high-latitude low-frequency pertur- bation(LFP)in the context of 1984～1986 ECMWF/WMO gridded data.Evidence suggests that the LFP's equivalent barotropic structure can be described in terms of a'structure parameter'(the ratio of low-frequency barotropic kinetic energy to low-frequency kinetic energy total);the high-value areas of the energy are closely associated with the zonal asymmetry and meridional shear of westerly jet;the LFP's propagation is marked by salient locality and conflu- ence/difluence,and can be interpreted by the counterclockwise loops of the central-Pacific low- frequency cyclone/anticyclone couplet(β-gyres);the Eastern-Asian longitudes at which westerly jet finds its entrance is the key region of interaction between NH mid-and low-latitude LFP's, on one side,and between bihemispheric counterparts;low-frequency vortex activity of mid-and high-latitude bears an intimate relation to the change in blocking,on the other.