Roles of initial ocean states on predicting the 2002/03 central Pacific El Niño
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摘要: 2002/03年厄尔尼诺事件,是暖海温中心出现在赤道中太平洋区域的一种新型厄尔尼诺,即中太平洋型厄尔尼诺。本文基于一个厄尔尼诺预测系统,利用三组回报试验来详细区分海洋表层和次表层初始状态对预报2002/03年中太平洋型厄尔尼诺事件的作用,并由此来探寻对预报厄尔尼诺演变过程最有利的初始条件。回报试验分为三组:(1)仅同化海表温度观测(sea surface temperature;简称SST)来优化海洋表层初始状态(Assim_SST);(2)仅同化海表高度观测(sea level;简称SL)来更新海洋次表层初始状态(Assim_SL);(3)同时同化SST和SL观测来一起更新海洋表层和次表层初始状态(Assim_SST+SL)。回报试验结果表明,三种不同的初始条件都可以使模式提前一年成功地预报2002/03年厄尔尼诺事件,并且"Assim_SST+SL"回报试验的效果最好。三组回报试验结果间的对比表明:海洋表层和次表层初始状态均对成功地预报该事件有重要作用,但其作用分别集中在事件发展的不同阶段。精确的海洋表层初始状态更容易激发模式预报出一次厄尔尼诺事件,而更合理的海洋次表层初始状态则能有效地提高厄尔尼诺事件预报的强度。Abstract: The 2002/03 El Niño event, a new type of El Niño with maximum warm anomaly occurring in the central equatorial Pacific, is known as central-Pacific (CP) El Niño. In this study, on the basis of an El Niño prediction system, roles of the initial ocean surface and subsurface states on predicting the 2002/03 CP El Niño event are investigated to determine conditions favorable for predicting El Niño growth and are isolated in three sets of hindcast experiments. The hindcast is initialized through assimilation of only the sea surface temperature (SST) observations to optimize the initial surface condition (Assim_SST), only the sea level (SL) data to update the initial subsurface state (Assim_SL), or both the SST and SL data (Assim_SST+SL). Results highlight that the hindcasts with three different initial states all can successfully predict the 2002/03 El Niño event one year in advance and that the Assim_SST+SL hindcast performs best. A comparison between the various sets of hindcast results further demonstrates that successful prediction is significantly affected by both of the initial surface and subsurface conditions, but in different developing phases of the 2002/03 El Niño event. The accurate initial surface state can easier trigger the prediction of the 2002/03 El Niño, whereas a more reasonable initial subsurface state can contribute to improving the prediction in the growth of the warm event.
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Key words:
- Initial oceanic states
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