The El Niño-Southern Oscillation (ENSO) is one of the most significant climate variability signals. Studying the changes in ENSO-induced precipitation variability (ENSO precipitation) in the past climate offers a possibility to a better understanding of how they may change under future climate conditions. This study uses simulations performed with the European community Earth-System Model (EC-Earth) to investigate the relative contributions of dynamic effect (the circulation anomalies together with the climatological specific humidity) and thermodynamic effect (the specific humidity anomalies together with the climatological circulation) on the changes in ENSO precipitation in the past warm and cold climates, represented by the Pliocene and the Last Glacial Maximum (LGM), respectively. The results show that the changes in ENSO precipitation are intensified (weakened) over the tropical western Pacific but weakened (intensified) over the tropical central Pacific in Pliocene (LGM) compared with the pre-industrial (PI) simulation. Based on the decomposed moisture budget equation, these changes in ENSO precipitation patterns are highly related to the dynamic effect. The mechanism can be understood as follows: the zonal gradient of the mean sea surface temperature (SST) over the tropical Indo-Pacific is increased (reduced) during the Pliocene (LGM), leading to the strengthening (weakening) of Pacific Walker Circulation as well as a westward (eastward) shift. In the Pliocene, the westward shift of Walker Circulation results in an increased (decreased) ENSO-induced low-level vertical velocity variability in the tropical western Pacific (central Pacific), and, in turn, favoring convergent (divergent) moisture transport through a dynamic process, and then causing intensified (weakened) ENSO precipitation there. The opposite mechanism exists in LGM. These results suggest that changes in the zonal SST gradient over tropical Indo-Pacific under different climate conditions determine the changes in ENSO precipitation through a dynamic process.

厄尔尼诺-南方涛动（ENSO）是最重要的气候变异信号之一。研究ENSO诱发的降水变化（ENSO降水）在过去的气候中的变化，可以更好地了解它们在未来气候条件下的变化。这项研究使用与欧洲共同体地球系统模型（EC-Earth）进行的模拟来研究动力效应（环流异常与气候比湿度）和热力学效应（比湿度异常与气候环比）的相对贡献）关于过去温暖和寒冷气候下ENSO降水的变化，分别以上新世和最后一次冰期最大值（LGM）为代表。结果表明，与工业化前的模拟相比，上新世（LGM）的热带西太平洋ENSO降水变化增强（减弱），而热带中太平洋的ENSO降水变化减弱（增强）。基于分解后的水分收支方程，ENSO降水模式的这些变化与动力效应高度相关。其机理可以理解如下：在上新世（LGM）期间，热带印度洋-太平洋上平均海面温度（SST）的纬向梯度增加（降低），导致太平洋沃克环流的增强（减弱）为：以及向西（向东）移动。在上新世，沃克环流向西移动会导致ENSO引起的热带西太平洋（中太平洋）低空垂直速度变化增加（减少），进而通过动态过程促进汇聚（发散）的水分输送，以及然后导致那里的ENSO降水增加（减弱）。LGM中存在相反的机制。这些结果表明，热带印度洋-太平洋在不同气候条件下纬向海温梯度的变化决定了ENSO降水通过动态过程的变化。