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This study compares an ensemble of seasonal hindcasts with a multidecadal integration from the same global coupled climate model over the tropical Pacific Ocean. It is shown that the annual mean state of the SST and its variability are different over the tropical Pacific Ocean in the two operating modes of the model. These differences are symptoms of an inherent difference in the physics of coupled air–sea interactions and upper ocean variability. It is argued that in the presence of large coupled model errors and in the absence of coupled data assimilation, the competing and at times additive influence of the initialization and model errors can change the behavior of the air–sea interaction physics and upper ocean dynamics. [ABSTRACT FROM AUTHOR]

Recent decadal regime shifts in the large-scale circulation of the tropical atmosphere are examined using analyses and independent observations of the circulation and precipitation. Comparisons between reanalysis products and independent observations suggest that the shifts that are apparent and significant in the reanalysis products may be artifacts of changes in the observing system and/or the data assimilation procedures. [ABSTRACT FROM AUTHOR]