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CN 11-1768/O4

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亚洲西风急流纬向非均匀性变化成因及其对东亚夏季气候的影响
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1.云南省西双版纳傣族自治州气象局;2.云南省景洪市气象局

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The Variation of Asian Westerly Jet Asymmetry and Its Impacts on East Asian Climate in Boreal Summer
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    摘要:

    利用美国国家海洋和大气管理局(NOAA)的CMAP月平均降水资料、NCEP/DOE 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(IAja),分析了夏季亚洲西风急流近41年来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温异常有关。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。

    Abstract:

    Based on the monthly mean rainfall data of CMAP and reanalysis of NCEP/DOE ⅡReanalysis form NOAA and the monthly precipitation and average temperature data from NMC,by defining an index (IAja) that is defined to describe the zonal asymmetric variation of Asian Westerly jet in upper troposphere, we have investigated the characteristics of the intensity difference between the east and west part of the Asian westerly jet and its climate impacts on East Asia from 1979 to 2019. The main conclusions are as follows: there are prominent inter-annual variations of the zonal asymmetry of Asian summer westerly jet, existing significant quasi-period of 6~8 years and 2 years. When the zonal asymmetry of Asian summer westerly jet is typically strong (weak), the wave-like anomalous rainfall pattern signed with the positive (negative)—negative (positive)—positive (negative) signs is observed form lower to higher latitudes in East Asia sector along with negative (positive) anomalies of temperature in the area of Lake Baikal,and simultaneously significant positive (negative) anomalies in regions including the Western area of China and Northern parts of Japan. The divergent and convergent wind components by the anomalous diabatic heating as a potential vorticity source directly induce the anomalies circulation in the mid-latitudes. The anomalous anticyclonic circulation making the intensity of west Asian jet increased and the eastern segment decreased help to the zonal asymmetry of Asian summer westerly jet stronger. The formation and facilitating of zonal asymmetric anomalies of the Asian jet are affected by not only convergence and divergence in the tropics and mid-latitudes, but also by wave energy propagating eastwards in westerlies. The eastward propagation of wave energy may be related to the SST anomaly of the Northern Atlantic. These results are helpful for us to better understand the formation mechanisms of the zonal asymmetry of Asian summer westerly jet.

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  • 收稿日期:2019-10-21
  • 最后修改日期:2020-05-10
  • 录用日期:2020-06-01
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