Two Major Modes of the Wintertime Precipitation over China
Two Major Modes of the Wintertime Precipitation over China
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发表时间：
2011
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通讯作者：
Wang Lin
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作者：
Wang Lin
基于中国160个站点的降水观测资料、NCEP/NCAR再分析数据和英国气象局Hadley中心的海温数据，利用经验正交函数（EOF）方法研究了中国冬季降水的两种主要模式，并利用线性回归方法研究了大气环流和海温的相关模式。结果表明，前两种EOF模态分别占总方差的49.6%和17.3%，可以很好地与其余模态分离。EOF1反映了中国东南部冬季降水的强度。相关主成分（PC1）在2 ~ 4年的周期内具有显著的年际变化。其年代际变化表明，20世纪80年代中期之前（之后）中国东南部冬季降水低于（高于）正常，近年来略有减少趋势。EOF2描述了华南与长江中下游及新疆北部的非相位关系。相关时间序列（PC2）也具有明显的2 ~ 4年周期和年代际分量，1980 ~ 2005年呈现明显的负极性变化趋势。进一步分析表明，EOF1与厄尔尼诺-南方涛动（ENSO）和东亚冬季风（EAWM）密切相关。当暖（冷）ENSO处于成熟阶段时，EAWM弱（强），来自孟加拉湾和南海的异常水汽输送在中国东南部辐合（辐散），有利于该地区降水增多（减少）。热带东太平洋海温异常与EOF1的变化有显著关系，可能是该模态的潜在预测因子。EOF2的变化与起源于北大西洋的横跨欧亚大陆的正压波列密切相关，该正压波列可引起中国东南沿海的异常北风（南风）。造成长江下游水汽通量辐散（辐合），华南水汽通量辐散（辐合），有利于EOF2正（负）相。北大西洋挪威海附近海温异常与EOF2的变化关系最为密切，可能是一个潜在的预测因子，其超前时间为7个月。
Based on the observed precipitation data from 160 China stations,the NCEP/NCAR reanalysis dataset and the sea surface temperature(SST) dataset from the Met Office Hadley Centre,this study investigates two major modes of wintertime precipitation over China through empirical orthogonal function(EOF) method and associated atmospheric circulation and SST through linear regression method.It reveals that the first two EOF modes account for 49.6% and 17.3% of the total variance,respectively,and can be well separated from the remaining modes.EOF1 reflects the strength of wintertime precipitation over southeastern China.The associated principal component(PC1) has significant interannual variability with 2-4 year period.Its interdecadal variations suggest that the wintertime precipitation over southeastern China was below(above) normal before(after) the mid-1980s,and has a slight decreasing trend in recent years.EOF2 delineates an out-of-phase relationship between South China and the middle and lower reaches of the Yangtze River as well as the northern part of Xinjiang.The associated time series(PC2) also has a clear 2-4 year period and an interdecadal component,which experiences a clear trend towards its negative polarity from 1980 to 2005.Further analysis suggests that EOF1 is closely related to the El Nio-Southern Oscillation(ENSO) and the East Asian winter monsoon(EAWM).When warm(cold) ENSO is in its mature phase,the EAWM is weak(strong),the anomalous water vapor transport from the Bay of Bengal and the South China Sea converges(diverges) over southeastern China and favors more(less) precipitation in this region.The SST anomalies over the tropical eastern Pacific have significant relationship with the variation of EOF1,and may act as a potential predictor for this mode.The variation of EOF2 is closely associated with a barotropic wave train across the Eurasian continent originating from the North Atlantic,which can induce anomalous northerlies(southerlies) along the coasts of southeastern China.It then causes the divergence(convergence) of water vapor flux in the lower reaches of the Yangtze River and opposite condition in South China,and therefore favors a positive(negative) phase of EOF2.The SST anomalies around the Norwegian Sea over the North Atlantic have the closest relationship with the variations of EOF2,and may act as a potential predictor with a leading time of 7 months.