SST 年循环对 El Ni?o 事件局地海气过程的影响

• 作 者: 李海燕 张文君 何金海 王亚兰
• 机 构: 南京信息工程大学气象灾害预报预警与评估协同创新中心气象灾害教育部重点实验室,
• 出 处: 海洋学报
• 发表日期: 2016年01期
• 关键词: El Ni?o annual cycle southward shift of atmospheric response

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 Nio海气相互作用过程的影响。尽管El Nio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 Nio年衰减阶段却有着强的向南移动特征。在El Nio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 Nio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 Nio事件大气响应有着至关重要的作用。

The effects of annual cycle on the El Nio air-sea interaction in the tropical Pacific Ocean are discussed using monthly sea surface temperatures at the Hadley Center, 10 m wind field at the European Center ERA-40, and CMAP precipitation data. Although the sea surface temperature anomaly corresponding to El Nio mainly appears in the equatorial eastern Pacific with a symmetrical north-south distribution, the corresponding atmospheric response of El Nio has a strong south-moving characteristic at the decay stage of El Nio. Strong westerly and precipitation anomalies mainly occurred in the equatorial Pacific Ocean before November of El Nio’s development. After December, the westerly and precipitation over the equator rapidly moved southward to 5 ° S, and the westerly wind persisted The location until the decline. At the same time, the negative anomalies of negative precipitation and anticyclones in the western Pacific move northward. This SST anomaly is not consistent with the meridional movement of its atmospheric response, mainly due to the seasonal southward shift of SST in the tropical Central Pacific climate. Due to the non-linear relationship between convection and SST, when the total SST exceeds a certain threshold, convective precipitation will rapidly increase; therefore, the corresponding convective response also moves southward with the SST, At the same time move south. In addition, the enhanced convection in the southern hemisphere further inhibits the precipitation in the northern hemisphere by meridional circulation, resulting in the anomalous and northward anomalies of negative precipitation and anti-cyclone in the western Pacific. The above conclusion is validated by analyzing two numerical experiments with / without annual cycles. That is, the experiment with annual cycles simulates the abnormal southwesterly anomalies in the observations and the anomalies in the northwestern Pacific anomalously. However, the annual cycle test Can simulate the westerly anomalies in the mid-equatorial Pacific during El Nio, but it does not move north-south, nor does the anti-cyclone in the northwestern Pacific appear. Therefore, the seasonal circulation of warm SST in the tropical Central Pacific plays an important role in the atmospheric response of El Nio event.