摘要
利用Hadley中心逐月海表温度、欧洲中心ERA-40的10m风场及CMAP降水资料探讨了年循环对热带太平洋El Nio海气相互作用过程的影响。尽管El Nio对应的海表温度异常主要出现在赤道东太平洋,经向上呈南北对称分布,然而其对应的大气响应在El Nio年衰减阶段却有着强的向南移动特征。在El Nio发展年的11月之前,强的西风和降水异常主要出现在赤道中太平洋;在12月份之后,赤道上的西风和降水异常迅速南移至5°S,随后西风一直维持在该位置直至衰亡。同时,西太平洋负降水和反气旋异常向北移动。这种SST异常与其大气响应的经向移动不一致,主要是由热带中太平洋气候态SST的季节性南移导致的。由于对流与海温之间存在非线性关系,即当总SST超过一定的阈值,对流降水才会迅速增强;因此相应的对流响应也随着总海温的南移而南移,风场响应也同时南移。此外,南半球增强的对流会通过经向环流进一步抑制北半球的降水,从而使西太平洋负降水和反气旋异常增强并北移。通过分析有/无年循环的两组数值试验结果验证了上述结论,即有年循环的试验较真实地模拟出了观测中异常西风南移和西北太平洋反气旋异常的出现;无年循环试验尽管能模拟出El Nio年赤道中太平洋的西风异常,但其却没有南北向的移动,西北太平洋的反气旋也没有出现。因此,热带中太平洋气候态暖海温的季节循环对El Nio事件大气响应有着至关重要的作用。
Influence of annual cycle on the local air-sea processes during El Nino events is investigated based on the Hadley Centre（HadISST1）sea surface temperature（SST）analysis data,10 mwind data from the European Centre for Medium-Range Weather Forecasts（ECMWF）ERA-40 reanalysis and the CMAP precipitation data.In the observation,SST anomalies associated with El Nino over the equatorial eastern Pacific are meridionally quasi-symmetric about the equator.However,corresponding atmospheric responses display a strong southward movement during the El Nino decaying phase.During the El Nino developing phase（largely before November）,almost meridionally symmetric zonal wind and precipitation anomalies are observed over the equatorial central Pacific.After the El Nino peak month（about December）,the equatorial westerly and precipitation anomalies shift rapidly southward with a center at about 5°S.Then the zonal wind anomalies stay there till the El Ninos termination.Meanwhile,negative precipitation and anticyclonic anomalies over the western Pacific shift northward.The inconsistence of the meridional movements of the El Nino SST anomalies and the associated atmospheric responses is mainly due to seasonally southward displacement of background warm SSTs along with the seasonal march of solar insolation.There is nonlinear relationship between convection and overall SST.That is,convective precipitation will be rapidly enhanced when total SST exceeds a certain threshold.Thus the corresponding convection anomalies are also displaced southward along with the southward shift of the SST and the zonal wind anomaly also appears south of the equator.In addition,the precipitation over northern hemisphere will be further suppressed due to the enhanced convection in southern hemisphere trough the meridional circulation,which can enhance the negative rainfall and anticyclone anomalies in the western Pacific and move northward.These observed analyses are supported by two experiments with and without considering the annual cycle.Southward shifts of the westerly anomalies and anticyclonic anomalies over the western North Pacific during the El Nino decaying phase are well simulated by the experiment with the annual cycle.However,these observed phenomena are not reproduced by the experiment without consideration of the annual cycle.Therefore,the annual cycle of climatological warm SSTs over the central Pacific plays a crucial role on the local atmospheric responses during the El Nino events.
出处
《海洋学报》
CAS
CSCD
北大核心
2016年第1期56-68,共13页
基金
国家重点基础研究发展计划973项目(2012CB417403)
公益性行业(气象)科研专项(GYHY 201506013,GYHY201406022)
江苏省研究生培养创新工程(CXZZ13_0505)
江苏省高校“青蓝工程”
关键词
EL
Nino
年循环
大气响应南移
El Nino
annual cycle
southward shift of atmospheric response
作者简介
李海燕（1983-），女，广西壮族自治区大新县人，博士，研究方向为ENSO动力学与海气相互作用。Email：ncl-talk@126．com
通信作者：张文君（1979-），男，教授，主要从事ENSO动力学、海陆气相互作用等方面研究。Email：zhangwj@nuist．edu．cn
