青藏高原和落基山脉对ENSO影响的比较研究

Comparison Studies of the Effect of Tibetan Plateau and Rocky Mountains on ENSO Variability

本文利用耦合气候模式研究了“有/无”青藏高原和落基山脉对厄尔尼诺—南方涛动(ENSO)的影响,并从温度变率方程的角度详细分析了ENSO变化的成因,结果表明:移除青藏高原或落基山脉均会造成ENSO变率增强;ENSO变率在无青藏高原试验中增强的幅度比在无落基山脉试验中更大。ENSO变率在地形敏感性试验中的变化与热带太平洋平均气候态的改变密切相关。移除青藏高原后热带太平洋信风减弱,大气对流中心东移,混合层变浅,温跃层变平,呈现出El Ni?o型海温分布,这些平均态的变化使海表风应力敏感性,Ekman抽吸敏感性以及温跃层敏感性幅度增强,最终导致ENSO振幅增大60%。然而,在移除落基山脉的情景下,热带太平洋信风变化更加复杂,大气对流中心稍有东移,混合层加深,温跃层变平,呈现出类La Ni?a型海温分布。这些变化增强了风应力敏感性和温跃层敏感性,最终导致ENSO振幅仅增大15%左右。本文研究表明,在地质时间尺度上青藏高原和落基山脉的抬升均抑制了ENSO变率。

In this study, the influence of the Tibetan Plateau and the Rocky Mountains on ENSO variability is investigated using a fully coupled climate model. Compared to that in the real world, the amplitude of ENSO variability becomes larger after removing the Tibetan Plateau or the Rocky Mountains. The ENSO amplitude is considerably stronger in a world without the Tibetan Plateau than that without the Rocky Mountains. The ENSO variability is closely linked with the mean climate in the tropical Pacific. The removal of the Tibetan Plateau results in weakened trade winds,an eastward shift of the atmospheric convection center, a shallower mixed layer depth, and an El Ni?o-like sea surface temperature(SST) distribution. These mean climate changes result in enhanced wind-stress sensitivity, Ekman upwelling sensitivity, and thermocline sensitivity, finally leading to a 60% increase in the ENSO amplitude. However, without the Rocky Mountains, the tropical Pacific shows a more complicated trade wind change, with a slight eastward shift of the atmospheric convection center, a deeper mixed layer depth, a flattened thermocline, and a La Ni?a-like SST distribution.These mean climate responses strengthen the wind stress and thermocline sensitivities, leading to a 10% increase in the ENSO amplitude. This study suggests that the uplift of the Tibetan Plateau and the Rocky Mountains during the geological period has played an important role in suppressing the ENSO variability.