中上新世是否存在“永久厄尔尼诺”状态——一个耦合模式结果

PERMANENT El Nino-LIKE CONDITIONS DURING THE MIDDLE PLIOCENE?——A COUPLED MODEL RESULTS

根据中上新世模拟比较计划(PlioMIP)试验设计方案,利用通用气候系统模式(CCSM4)低分辨率版本就该时期是否存在"永久厄尔尼诺"状态给予了数值模拟研究。结果表明,相对于工业革命前期,中上新世海洋表面温度(SST)在赤道太平洋地区东部比西部增温显著,导致赤道太平洋地区东西方向上的SST梯度减弱;然而,模拟的中上新世热带太平洋SST仍然以厄尔尼诺/南方涛动(ENSO)循环为主,且ENSO循环并未减弱,换言之,试验结果不支持中上新世存在"永久厄尔尼诺"状态。

There are still uncertainties for permanent E1 Nifio existing in Middle Pliocene. Based on the Pliocene Model Intercomparison Project, the scientific topic of whether or not permanent E1 Nifio exists in the mid-Pliocene is investigated using the Community Climate System Model version 4 （CCSM4）, a coupled ocean-atmosphere general circulation model. Model results show that the sea surface temperature （SST）warming is stronger in the eastern equatorial Pacific than that in the western equatorial Pacific,resulting in a reduced west to east SST gradient in the equatorial Pacific during the mid-Pliocene. Because of limited reduced SST gradient, the pattern with high SST in the western equatorial Pacific and low SST in the eastern equatorial Pacific does not change. Moreover,the regional change of other climate variables is also closely related with the changed west to east SST gradient in equatorial Pacific. Besides, the equatorial Pacific SSTs are also characterized by an E1 Nino-Southern Oscillation（ENSO） mode in the mid-Pliocene simulation and the ENSO in the mid-Pliocene is not weaker relative to the pre-industrial. In both mid-Pliocene and pre-industrial simulations, the period of ENSO is also similar to each other. In summary, model results show that permanent E1 Nino conditions do not exist in the mid-Pliocene.