Characterization of the Different El Niño Types and their Impacts in South America From Observed and Modeled Data

Abstract Recent studies have pointed out to the existence of two El Niño (EN) types: Eastern Pacific or Canonical (EP) EN and Central Pacific or Modoki (CP) EN. In the present study, the observed and simulated data in three models of the Coupled Model Intercomparison Project phase 5 (CMIP5) were used to evaluate the impacts of two EN types on the South American precipitation from June-August of the EN onset year to March-May of the following year. The Centre National de Recherches Météorologiques (CNRM-CM5) model presented a better performance in reproducing the observed SST anomaly patterns for the CP and EP EN types. The observed precipitation anomaly pattern associated with the EN events was better represented during the austral summer. In the case of the EP EN, such pattern features wetness (dryness) in southeastern (northern-northwestern) South America. The CNRM-CM5 and Hadley Centre Global Environmental Model (HadGEM2-ES) models reproduced this pattern. The Max Planck Institute Earth System Model (MPI-ESM-LR) model reproduced the dryness over northern, but not the rainfall increasing in southeastern and the rainfall reduction in northwestern of the continent. In the case of the CP EN, the observed impact on the South American rainfall during the austral summer featured rainfall scarcity (excess) in northern and northwestern (southeastern) South America. The models reproduced this pattern, however, the HadGEM2-ES and MPI-ESM-LR models showed lower rainfall over northeastern Brazil than the observed one. The EN teleconnection differences explain the differences of the simulated patterns.

摘要 近期研究指出存在两类厄尔尼诺（El Niño，简称EN）：东太平洋型（经典型，EP）厄尔尼诺与中太平洋型（Modoki型，CP）厄尔尼诺。本研究采用耦合模式比较计划第五阶段（Coupled Model Intercomparison Project Phase 5，CMIP5）的3个模式的观测与模拟数据，评估两类厄尔尼诺事件从发生年6-8月至次年3-5月对南美降水的影响。法国国家气象研究中心模式（CNRM-CM5，Centre National de Recherches Météorologiques）在复现CP与EP型厄尔尼诺的观测海表温度异常分布方面表现更优。观测到的与厄尔尼诺事件相关的降水异常分布，在南半球夏季的再现效果更佳。就EP型厄尔尼诺而言，该异常分布表现为南美东南部偏湿、北部至西北部偏干。CNRM-CM5与哈德利中心全球环境模式（HadGEM2-ES，Hadley Centre Global Environmental Model）能够复现这一分布特征。马克斯·普朗克研究所地球系统模式（MPI-ESM-LR，Max Planck Institute Earth System Model）仅再现了南美北部的偏干特征，未能复现东南部降水增加与西北部降水减少的现象。就CP型厄尔尼诺而言，南半球夏季观测到的南美降水影响表现为北部与西北部降水偏少、东南部降水偏多。各模式均复现了这一分布，但HadGEM2-ES与MPI-ESM-LR模式模拟的巴西东北部降水较观测值偏低。厄尔尼诺遥相关的差异可解释各模拟结果间的分布差异。