Can the Southern Hemisphere annular mode affect China winter monsoon
Can the Southern Hemisphere annular mode affect China winter monsoon
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DOI：
10.1029/2008jd011501
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发表时间：
2009-06
影响因子：
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通讯作者：
Zhiwei Wu;Jianping Li;Bin Wang;Xinhua Liu
中科院分区：
文献类型：
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作者：
Zhiwei Wu;Jianping Li;Bin Wang;Xinhua Liu
[1] 先前的许多研究表明，异常的北半球环模（NAM）和相关的低边界强迫（例如积雪）极大地影响了中国冬季风（CWM）的年际至年代际时间尺度的变化。本文发现南半球环模（SAM）与观测到的两个CWM主模也有很好的相关性，这是以前从未揭示过的。请注意，CWM 的两个主要模态是通过对 1951 年至 2006 年期间中国 160 个监测站的冬季地表气温进行经验正交函数 (EOF) 分析而获得的。他们解释了大约 70% 的 CWM 总方差。第一个EOF模态表现出均匀的空间格局，相应的主成分呈现显着的年代际变化，反映了过去56年中国变暖的趋势。第二个EOF模态呈现出经向跷跷板模式，并且基本上与显着的年际变化相关。两种主导模态都与同时发生的类SAM半球环流异常密切相关。此外，类SAM异常为北半球秋季第一个CWM模态提供了先兆条件。利用 NCAR 社区大气模型版本 3 (CAM3) 研究了异常秋季 SAM 可能影响 CWM 的相关物理机制。当北半球秋季南半球环状模（SAM）处于强位相时，环南极上层急流向极地移动，相应的表面风速在45S至30S之间的区域降低，从而在下方产生半球规模的温暖海面温度（SST）带。这种异常温暖的海温带会持续整个北半球冬季，并削弱哈德来环流环流。北半球冬季哈德来环流减弱与中国上空对流层低层盛行的异常南风相对应，有利于CWM减弱。秋季 SAM 和 CWM 之间的密切联系可能有助于了解北半球和南半球之间的相互作用，并可以提供预测 CWM 变化的方法。
[1] Many previous studies suggested that the anomalous Northern Hemisphere annular mode (NAM) and associated low boundary forcing (e.g., snow cover) greatly influence the China winter monsoon (CWM) variability on interannual to inter-decadal timescales. In this article, it is found that the Southern Hemisphere annular mode (SAM) also well correlates with the two observed CWM major modes, which has not been revealed before. Note that the two CWM major modes are obtained by performing Empirical Orthogonal Function (EOF) analysis on winter surface air temperature at 160 gauge stations across China for the 1951–2006 period. They explain around 70% of the total CWM variances. ThefirstEOFmodeexhibitsahomogeneousspatialpatternwiththecorrespondingprincipal component displaying a significant inter-decadal variation, which reflects the warming trend in China during the past 56 years. The second EOF mode shows a meridional seesaw patternandisbasicallyassociatedwithsignificantinterannualvariations.Bothoftheleading modes are intimately associated with the simultaneous SAM-like hemispheric circulation anomalies.Moreover,theSAM-likeanomaliessignalprecursoryconditionsforthefirstCWM mode in boreal autumn. The relevant physical mechanisms by which anomalous autumn SAM may affect the CWM are investigated with NCAR Community Atmospheric Model version 3 (CAM3). When SAM is in a strong phase during boreal autumn, the circumAntarctic upper level jet stream displaces poleward and the corresponding surface wind speeds reduce in the region between 45S and 30S, inducing a hemispheric-scale warm sea surface temperature (SST) belt beneath. Such an anomalously warm SST belt persists through boreal winter and weakens the Hadley cell. The weakened Hadley cell in boreal wintercorrespondstoanomaloussoutherliesprevailinginthelowertroposphereoverChina, which favor a weak CWM. The intimate linkage between the autumn SAM and CWM may be instrumental for understanding interactions between the Northern and Southern Hemisphere and can provide a way to predict the CWM variations.