Sayaka Yasunaka

An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC

Decadal climate predictability is examined in hindcast experiments by a multi-model ensemble using three versions of the coupled atmosphere-ocean model MIROC. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity with prescribed natural and anthropogenic forcings on the basis of the historical data and future emission scenarios in the Intergovernmental Panel of Climate Change. Results of the multi-model ensemble in our hindcast experiments show that predictability of surface air temperature (SAT) anomalies on decadal timescales mostly originates from externally forced variability. Although the predictable component of internally generated variability has considerably smaller SAT variance than that of externally forced variability, ocean subsurface temperature variability has predictive skills over almost a decade, particularly in the North Pacific and the North Atlantic where dominant signals associated with Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are observed. Initialization enhances the predictive skills of AMO and PDO indices and slightly improves those of global mean temperature anomalies. Improvement of these predictive skills in the multi-model ensemble is higher than that in a single-model ensemble.

North Pacific dissolved inorganic carbon variations related to the Pacific Decadal Oscillation

We elucidated multiyear variations of sea surface dissolved inorganic carbon (DIC) concentrations in the North Pacific from 2002 to 2008 by using monthly DIC maps derived from partial pressure CO2 observations. The Pacific Decadal Oscillation (PDO) was related to an east-west seesaw pattern in the North Pacific DIC anomaly field. In the western North Pacific, DIC concentrations were relatively high from mid-2002 to mid-2005 and low after late 2007 compared with climatological values, and in the eastern North Pacific the opposite change was observed. Changes of the forcing factors associated with the PDO could explain the DIC east-west seesaw pattern: horizontal advection, freshwater fluxes and vertical mixing in most regions, CO2 fluxes south of 40°N, and biological production in the subarctic.