doi:  10.3878/j.issn.1006-9895.1911.19141

Contribution of Tropical and Subtropical Circulation Anomalies to the Intensity of East Asian Winter Monsoon over Lower-latitude Region
摘要点击 165  全文点击 32  投稿时间:2019-04-11  修订日期:2019-08-19
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基金:  国家自然科学基金
中文关键词:  东亚冬季风  热带环流 副热带环流  低纬度冬季风
英文关键词:  East  Asian winter  monsoon, Tropical  circulation, Subtropical  circulation, Low-latitude  EAWM
彭京备Peng Jingbei中国科学院大气物理研究所
刘舸Liu Ge中国气象科学研究院灾害天气国家重点实验室,北京,100081
孙淑清Sun Shuqing中国科学院大气物理研究所
Citation:Peng Jingbei,Liu Ge,Sun Shuqing.2020.Contribution of Tropical and Subtropical Circulation Anomalies to the Intensity of East Asian Winter Monsoon over Lower-latitude Region[J].Chinese Journal of Atmospheric Sciences (in Chinese)
      The East Asian winter monsoon (EAWM) has two dominant modes: the in-phase and out-of-phase variations of wind anomalies over northern and southern China. Different from the first mode reflecting a uniform strong/weak situation of the EAWM throughout eastern China, the second mode indicates a situation that the intensity of low-latitude EAWM over southern China is independent from and even opposite to that of mid-high-latitude EAWM over northern China. The present study focuses on the characteristics of tropical and subtropical circulation anomalies associated with the variability of low-latitude EAWM under the background of the second mode. The results reveal that the inter-tropical convergence zone (ITCZ) can be considered as an important circulation system that contributes to the variation of low-latitude EAWM. Corresponding to a stronger and northward-extended ITCZ, convective ascending over the tropical western Pacific and South China Sea is strengthened. This anomalous ascending may induce low-level anomalous northerly wind, thus resulting in a stronger low-latitude EAWM. In addition, the subtropical upper-level jet can be regarded as another important circulation system affecting the low-latitude EAWM. An increase in wind speed along the axis of the jet may cause anomalous quasi-geostrophic northerly near the entrance of the jet. Associated with the forced positive secondary circulation anomaly with anomalous descending (ascending) to the north (south) of the jet, the low-level anomalous northerly appears under the jet, in turn, facilitates a stronger low-latitude EAWM. Finally, both the individual and joint effects of tropical convective activities and upper-level subtropical jet on the low-latitude EAWM are further investigated. Relatively, the influence of ITCZ seems more important. When the two circulation anomalies simultaneously enhance (i.e., more active convective of ITCZ and stronger wind speed along the subtropical upper-level jet), their joint effect can significantly reinforce northerly winds to the south of 35°N, over southern China, and vice versa. The above-mentioned results imply that, the variability of low-latitude EAWM is not only affected by cold air surges from northern China, but also modulated by the joint effects of tropical and subtropical circulation anomalies.
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