摘要
摘要:利用美国NOAA（National Oceanic and Atmospheric Administration）的CMAP（Climate Prediction Center (CPC) Merged Analysis of Precipitation）月平均降水资料、NCEP/DOE（National Centers for Environmental Prediction/Design of Experiments）II的月平均再分析资料和中国气象局国家信息中心提供的中国160站逐月降水和平均气温资料，通过定义一个亚洲急流纬向非均匀性指数（I_Aja），分析了1979～2019年夏季亚洲西风急流纬向非均匀性的年际变化特征，揭示了夏季亚洲急流纬向非均匀性变化异常的成因及其对东亚夏季降水和气温的影响。结果表明：夏季亚洲西风急流纬向非均匀性具有显著的年际变化特征，并存在6～8年和2年左右的振荡周期。当急流纬向非均匀性典型偏强（弱）年，东亚东部地区从低纬到高纬，降水异常主要呈现出偏多—偏少—偏多（偏少—偏多—偏少）的经向分布；气温则在中国西部地区和日本北部偏高（低），贝加尔湖地区偏低（高）。引起夏季亚洲急流纬向非均匀性异常的可能原因如下：由大气非绝热加热异常而引起的热带和中纬度地区辐合/辐散运动造成的涡度源强迫，和来自西风带中波扰动能量的注入，两者共同作用形成并维持了与急流纬向非均匀性强弱变化相联系的异常环流，从而使亚洲急流东、西段强度差异增强（减弱），进而有利于急流纬向非均匀性异常偏强（偏弱）。而上述西风带中波扰动能量的东传可能与北大西洋海表面温度异常有关。这对于深刻理解夏季亚洲急流纬向非均匀性异常的形成机理提供了有用的线索。
关键词:亚洲西风急流/
纬向非均匀性/
东亚气候/
夏季
Abstract:Based on CMAP (Climate Prediction Center (CPC) Merged Analysis of Precipitation) monthly mean rainfall data and NCEP/DOE (National Centers for Environmental Prediction/Design of Experiments) II Reanalysis data from NOAA (National Oceanic and Atmospheric Administration) and the monthly precipitation and average temperature data from NMIC (National Meteorological Information Center), the authors defined an index (I_Aja) that describes the zonal asymmetric variation of the Asian westerly jet in the upper troposphere, from which the authors investigated the characteristics of the intensity difference between the eastern and western parts of the Asian westerly jet and its impacts on the climate of East Asia from 1979 to 2019. The conclusions are as follows: There are prominent interannual variations in the zonal asymmetry of the Asian summer westerly jet, with significant quasi-periods of 6–8 years and 2 years. When the zonal asymmetry of the Asian summer westerly jet is typically strong (weak), the wave-like anomalous rainfall pattern generates positive (negative)—negative (positive)—positive (negative) signs in the lower to higher latitudes in the East Asia sector along with negative (positive) temperature anomalies in the Lake Baikal area, and simultaneously significant positive (negative) anomalies in regions in West China and North Japan. The divergent and convergent wind components by the anomalous diabatic heating as a potential vorticity source directly induce the circulation anomalies in the mid-latitudes. The anomalous anticyclonic circulation causes the intensity of the west Asian jet to increase and the eastern segment to decrease, which strengthens the zonal asymmetry of the Asian summer westerly jet. The formation of and support provided by the zonal asymmetric anomalies of the Asian jet are affected by their convergence and divergence in the tropics and mid-latitudes, as well as the eastward propagation of wave energy in the westerlies. This eastward propagation of wave energy may be related to the sea surface temperature anomaly of the Northern Atlantic. These results facilitate a better understanding of the formation mechanisms of the zonal asymmetry of the Asian summer westerly jet.
Key words:Asian westerly jet/
Zonal asymmetry/
East Asian climate/
Boreal summer



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