Asymmetry of Atmospheric Circulation Anomalies over the Western North Pacific between El Nino and La Nina
Asymmetry of Atmospheric Circulation Anomalies over the Western North Pacific between El Nino and La Nina
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DOI：
10.1175/2010jcli3222.1
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发表时间：
2010-09
影响因子：
4.9
通讯作者：
Bo Wu;Tim Li;Tianjun Zhou
中科院分区：
文献类型：
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作者：
Bo Wu;Tim Li;Tianjun Zhou
研究了厄尔尼诺和拉尼娜成熟冬季西北太平洋低层大气环流异常的不对称性。拉尼娜期间的异常WNP气旋(WNPC)中心相对于厄尔尼诺期间的WNP反气旋(WNPAC)中心有向西移动的趋势。有两个因素可能会导致这种不对称的反应。第一个因素是厄尔尼诺和拉尼娜异常加热的纵向移位。拉尼娜-S期间的合成降水负距平中心位于厄尔尼诺期间合成正降水异常中心的西侧。加热的西移可能会进一步推动西北风相对于西北风的位置向西移动。二是西北太平洋海温异常的幅度不对称性，即厄尔尼诺期间局地冷海温异常的幅度大于拉尼娜期间暖海温异常的幅度。海温异常的不对称性源于ENSO发展夏季海温异常的不对称趋势。尽管降水和地面风异常都是近似对称的，但在气候平均纬向风速较小的关键WNP区，地面潜热通量异常是高度不对称的。厄尔尼诺期间的异常西风和拉尼娜期间的异常东风都导致了地面蒸发的增强，增强(减弱)了厄尔尼诺(拉尼娜)期间就地冷(暖)海温的增强。厄尔尼诺和拉尼娜在成熟冬季的异常风速差异进一步放大了西北太平洋海温异常的不对称性。大气环流模式实验表明，这两个因素都是造成WNPAC和WNPC之间不对称性的原因。厄尔尼诺和拉尼娜之间时间演变的不对称性是由于西北地区环流的不对称性造成的。
The asymmetry of the western North Pacific (WNP) low-level atmospheric circulation anomalies between the El Nino and La Nina mature winter is examined. An anomalous WNP cyclone (WNPC) center during La Nina tends to shift westward relative to an anomalous WNP anticyclone (WNPAC) center during El Nino. Two factors may contribute to this asymmetric response. Thefirst factor is the longitudinal shifting of El Nino and La Nina anomalous heating. The composite negative precipitation anomaly center during La Ninai s located farther to the west of the composite positive precipitation anomaly center during El Nino. The westward shift of the heating may further push the WNPC westward relative to the position of the WNPAC. The second factor is the amplitude asymmetry of sea surface temperature anomalies (SSTAs) in the WNP, namely, the amplitude of local cold SSTA during El Nino is greater than that of warm SSTA during La Nina. The asymmetry of SSTA is originated from the asymmetric SSTA tendencies during the ENSO developing summer. Although both precipitation and surface wind anomalies are approximately symmetric, the surface latent heat flux anomalies are highly asymmetric over the key WNP region, where the climate mean zonal wind speed is small. Both the anomalous westerly during El Nino and the anomalous easterly during La Nina in the region lead to an enhanced surface evaporation, strengthening (weakening) the enhancement of the cold (warm) SSTA in situ during El Nino (La Nina). The asymmetry of the SSTA in the WNP is further amplified due to anomalous wind differences between El Nino and La Nina in their mature winter. Atmo- spheric general circulation model experiments demonstrate that both factors contribute to the asymmetry between the WNPAC and WNPC. The asymmetric circulation in the WNP contributes to the asymmetry of temporal evolutions between El Nino and La Nina.