Seasonally evolving dominant interannual variability modes of East Asian climate.
Seasonally evolving dominant interannual variability modes of East Asian climate.
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DOI：
10.1175/2008jcli2710.1
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发表时间：
2009-06
影响因子：
4.9
通讯作者：
Bo Wu;Tianjun Zhou;Tim Li
中科院分区：
文献类型：
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作者：
Bo Wu;Tianjun Zhou;Tim Li
对1979 - 2004年期间东亚地区的季节平均降水进行了季节依赖型经验正交函数（S - EOF）分析。前两个主导模态占年际总方差的44%，分别对应于ENSO之后和ENSO转折年份。第一模态表明，在厄尔尼诺衰减的夏季，北太平洋西部（WNP）上空出现异常反气旋。该反气旋与从中国中部到日本南部的强正降水异常有关。在接下来的秋季，由于前一个夏季短波辐射通量增加导致的海表温度（SST）正异常，WNP上空出现对流增强。中国东南部出现干旱情况。这种异常降水模式在随后的冬季和春季持续存在。第二模态显示，在厄尔尼诺发展的夏季，赤道中太平洋的异常加热在WNP上空强迫出一个气旋性涡度。这加强了WNP季风。同时，在北印度洋有一个异常反气旋发展，并在随后的秋季和冬季向东移动到南海和WNP。这导致中国东南部降水增加。通过局地海 - 气相互作用，反气旋和降水异常在接下来的春季得以维持。对高层速度势和中层垂直运动场的诊断揭示了一种季节依赖型的印度洋强迫情景。在厄尔尼诺成熟的冬季和随后的春季，印度洋全海域变暖对WNP的异常环流没有显著影响，因为热带印度洋上的对流受到赤道中东太平洋的遥强迫抑制。在厄尔尼诺衰减的夏季，全海域变暖通过大气开尔文波或哈德利环流在影响WNP异常反气旋方面起到积极作用。
A season-reliant empirical orthogonal function (S-EOF) analysis is applied to seasonal mean precipitation over East Asia for the period of 1979-2004. The first two dominant modes account for 44% of the total interannual variance, corresponding to post-ENSO and ENSO turnabout years, respectively. The first mode indicates that in El Nino decaying summer, an anomalous anticyclone appears over the western North Pacific (WNP). This anticyclone is associated with strong positive precipitation anomalies from central China to southern Japan. In the following fall, enhanced convection appears over the WNP as a result of the un- derlying warm SST anomalies caused by the increase of the shortwave radiative flux in the preceding sum- mer. A dry condition appears over southeastern China. The anomalous precipitation pattern persists throughout the subsequent winter and spring. The second mode shows that during the El Nino developing summer the anomalous heating over the equatorial central Pacific forces a cyclonic vorticity over the WNP. This strengthens the WNP monsoon. Meanwhile, an anomalous anticyclone develops in the northern Indian Ocean and moves eastward to the South China Sea and the WNP in the subsequent fall and winter. This leads to the increase of precipitation over southeastern China. The anticyclone and precipitation anomalies are maintained in the following spring through local air-sea interactions. The diagnosis of upper-level velocity potential and midlevel vertical motion fields reveals a season- dependent Indian Ocean forcing scenario. The Indian Ocean basinwide warming during the El Nino mature winter and the subsequent spring does not have a significant impact on anomalous circulation in the WNP, because convection over the tropical Indian Ocean is suppressed by the remote forcing from the equatorial central-eastern Pacific. The basinwide warming plays an active role in impacting the WNP anomalous an- ticyclone during the ENSO decaying summer through atmospheric Kelvin waves or Hadley circulation.