The Effect of the South Pacific Convergence Zone on the Termination of El Nino Events and the Meridional Asymmetry of ENSO
The Effect of the South Pacific Convergence Zone on the Termination of El Nino Events and the Meridional Asymmetry of ENSO
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DOI：
10.1175/jcli-d-11-00332.1
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发表时间：
2012-08-15
影响因子：
4.9
通讯作者：
England, Matthew H.
中科院分区：
文献类型：
--
作者：
McGregor, Shayne;Timmermann, Axel;England, Matthew H.
在大型厄尔尼诺事件中，西风对赤道东太平洋海面温度异常（SSTAs）的响应在北方冬季和早春期间向南转移，达到纬度5°-7°s。由此产生的经向不对称以及赤道风异常的相关季节性减弱是强厄尔尼诺事件终止的关键因素。利用一个中等复杂的大气模式表明，这些特征是由于赤道以南的气候风速在历年年底减弱所致。与南太平洋辐合带（SPCZ）季节性增强相关的气候风速降低，导致边界层Ekman泵送异常，边界层/对流层低层风对El Nino联合响应的地面动量阻尼减小。这使得相关的纬向风异常向赤道以南移动。此外，利用线性浅水海洋模式表明，南风转移对纬向赤道平均热含量的变化起着重要作用，并且是ENSO循环（补给/排放）阶段温跃层深度经向不对称的唯一原因。这一结果质疑了海洋罗斯比波在厄尔尼诺事件相位同步终止中的唯一作用，并提出12 - 2月/ 3 - 5月真实气候SPCZ （DJF/MAM）的发展是强厄尔尼诺事件季节性终止的关键因素之一。
During large El Nino events the westerly wind response to the eastern equatorial Pacific sea surface temperature anomalies (SSTAs) shifts southward during boreal winter and early spring, reaching latitudes of 5 degrees-7 degrees S. The resulting meridional asymmetry, along with a related seasonal weakening of wind anomalies on the equator are key elements in the termination of strong El Nino events. Using an intermediate complexity atmosphere model it is demonstrated that these features result from a weakening of the climatological wind speeds south of the equator toward the end of the calendar year. The reduced climatological wind speeds, which are associated with the seasonal intensification of the South Pacific convergence zone (SPCZ), lead to anomalous boundary layer Ekman pumping and a reduced surface momentum damping of the combined boundary layer/lower-troposphere surface wind response to El Nino. This allows the associated zonal wind anomalies to shift south of the equator. Furthermore, using a linear shallow-water ocean model it is demonstrated that this southward wind shift plays a prominent role in changing zonal mean equatorial heat content and is solely responsible for establishing the meridional asymmetry of thermocline depth in the turnaround (recharge/discharge) phase of ENSO. This result calls into question the sole role of oceanic Rossby waves in the phase synchronized termination of El Nino events and suggests that the development of a realistic climatological SPCZ in December-February/March-May (DJF/MAM) is one of the key factors in the seasonal termination of strong El Nino events.