Evaluation of performance of CMIP5 models in simulating the North Pacific Oscillation and El Nino Modoki

Abstract

Previous observational studies have documented that the occurrence frequency of El Nino Modoki is closely linked to the North Pacific Oscillation (NPO). The present paper evaluates the relationships between the frequency of El Nino Modoki and the NPO in the historical runs of the Coupled Model Intercomparison Project Phase 5 (CMIP5) and examines the related physical processes. It is found that six of 25 CMIP5 models can reproduce both the spatial patterns of the NPO and El Nino Modoki. Four of these six models exhibit good performance in simulating the positive correlation between the NPO index and the frequency of El Nino Modoki. The analyses further show that the key physical processes determining the relationships between the NPO and the frequency of El Nino Modoki are the intensity of wind-evaporation-SST (WES) feedback in the subtropical northeastern North Pacific. This study enhances the understanding of the connections between the North Pacific mid-latitude climate system and El Nino Modoki, and has an important implication for the change of El Nino Modoki under global warming. If global warming favors to produce an oceanic and atmospheric pattern similar to the positive phase of the NPO in the North Pacific, more El Nino Modoki events will occur in the tropical Pacific with the assistance of the WES feedback processes.