Improved simulation of Pacific Decadal Oscillation in CMIP5 models: Effect of ENSO teleconnection

Abstract

Pacific decadal oscillation (PDO), a dominant decadal variability in the North Pacific, not only affects the Northeast Pacific marine ecosystems but also interacts with various oceanic and atmospheric processes. Recently, model comparison studies using coupled climate models show that a representation of PDO has been improved by the Coupled Model Intercomparison Project - phase 5 (CMIP5) models as compared with the phase 3 (CMIP3) models. We found that this improvement of PDO representation can be characterized by a notable enhancement of the magnitude of the central PDO which is known for its close link to an atmospheric forcing by teleconnections from the tropical Pacific. Here we aim to investigate the factors affecting the PDO improvement with a focus on the tropical forcing associated with El Ni&ntilde o - Southern Oscillation (ENSO). Tropical deep convection, an indicator of the tropical forcing, was found to be improved from CMIP3 to CMIP5, indicating an enhanced excitation of equatorial waves which directly affect the North Pacific atmosphere and ocean. Our findings suggest that this enhancement of the North Pacific oceanic and atmospheric variabilities related to ENSO corresponds to the improvement of the central PDO magnitude. The results indicate that the improved PDO representation is mainly attributed to the more strongly connected dynamical link between tropics and extra-tropics, implying that it would tudies using coupled climate models show that a representation of PDO has been improved by the Coupled Model Intercomparison Project - phase 5 (CMIP5) models as compared with the phase 3 (CMIP3) models. We found that this improvement of PDO representation can be characterized by a notable enhancement of the magnitude of the central PDO which is known for its close link to an atmospheric forcing by teleconnections from the tropical Pacific. Here we aim to investigate the factors affecting the PDO improvement with a focus on the tropical forcing associated with El Ni&ntilde o - Southern Oscillation (ENSO). Tropical deep convection, an indicator of the tropical forcing, was found to be improved from CMIP3 to CMIP5, indicating an enhanced excitation of equatorial waves which directly affect the North Pacific atmosphere and ocean. Our findings suggest that this enhancement of the North Pacific oceanic and atmospheric variabilities related to ENSO corresponds to the improvement of the central PDO magnitude. The results indicate that the improved PDO representation is mainly attributed to the more strongly connected dynamical link between tropics and extra-tropics, implying that it would