摘要:利用中国北方季风区46站盛夏降水观测资料，采用经验正交函数分解（EOF）、合成分析和相关分析等方法，将盛夏北方季风区划分为4类雨型：A型全区一致偏多、B型全区一致偏少、C型华北偏多东北偏少和D型华北偏少东北偏多，并对比分析了四类雨型同期大气环流和前期至同期海温演变特征的差异，以探讨其形成机制及前期预测信号。结果表明：四类雨型对应的东亚大气环流和海温演变具有明显的差异。A型年：东亚副热带西风急流（西风急流）和西太平洋副热带高压（西太副高）位置偏北，东亚夏季风偏强，欧亚中高纬以纬向环流为主，北方季风区低层辐合、高层辐散，冷暖空气在北方季风区辐合；从前冬至夏季，赤道中东太平洋类似于东部型La Ni?a发展年的海温异常分布，北大西洋海温三极子模态（NAT）负位相逐渐形成；B型年则基本相反。C（D）型年：西风急流异常偏北（略偏南），西太副高偏西（东）偏北，华北盛行西南（西北）风，东北盛行东北（东南）风，华北地区对流层低层辐合（辐散）高层辐散（辐合），东北地区对流层低层辐散（辐合）高层辐合（辐散），东北冷涡较弱（活跃）；从前冬至夏季，赤道中东太平洋和印度洋逐渐由暖海温向冷海温转变（El Ni?o分布形态逐渐形成）。
关键词:北方季风区/
雨型/
大气环流/
海温演变
Abstract:Based on the precipitation observation data of 46 stations in the northern China monsoon region (NCMR) and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis datasets, the midsummer rainfall patterns in the NCMR during 1961–2019 are objectively classified into four typical categories: pattern A, pattern B, pattern C, and pattern D. Pattern A (B) corresponds to the positive (negative) anomaly midsummer precipitation in the whole area, while pattern C (D) corresponds to positive (negative) anomaly precipitation in North China (Northeast China). The characteristics of the four rainfall patterns, atmospheric circulation, sea surface temperature (SST), and precursors are investigated with EOF and composite analysis along with other methods. The major circulation characteristics and the evolution of SST, resulting in the four rainfall patterns, are different. Pattern A: The East Asia subtropical westerly jet stream (EAJS) shows a northward trend relative to its normal position. The ridgeline of the western Pacific subtropical high (WPSH) is located to the north of its normal position, accompanying stronger southerly winds. The zonal circulation is dominant in the middle and high latitudes of Eurasia. There are significant convergences (divergences) at the low (high) level in the troposphere and cold and warm air convergence in the NCMR. The negative phase of the North Atlantic SST tripole and the eastern pattern of La Ni?a develop from the previous winter to summer. Meanwhile, the characteristics of atmospheric circulation and SST evolution of pattern B are basically opposite to those of pattern A. Pattern C (D): EAJS shows an anomalous northward (slight southward) trend relative to its normal position. The longitudinal position of WPSH is located westward (eastward), and their ridgelines both tend to be northward of the normal position. North China is controlled by stronger southwest (northwest) winds, while northeast (southeast) winds prevail over northeast China. The lower troposphere converges (diverges) and the upper troposphere diverges (converges) in North China, while the lower troposphere diverges (converges) and the upper troposphere converges (diverges) in northeast China, accompanying a weak (active) northeast cold vortex. Meanwhile, the warm SST transforms to cold SST (El Ni?o pattern gradually forms) in the middle eastern tropical Pacific.
Key words:Northern China monsoon region/
Rainfall pattern/
Atmospheric circulation/
SST evolution
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