Abstract
Decadal climate predictability in the South Atlantic is explored by performing reforecast experiments using a coupled general circulation model with two initialization schemes; one is assimilated with observed sea surface temperature (SST) only, and the other is additionally assimilated with observed subsurface ocean temperature and salinity. The South Atlantic is known to undergo decadal variability exhibiting a meridional dipole of SST anomalies through variations in the subtropical high and ocean heat transport. Decadal reforecast experiments in which only the model SST is initialized with the observation do not predict well the observed decadal SST variability in the South Atlantic, while the other experiments in which the model SST and subsurface ocean are initialized with the observation skillfully predict the observed decadal SST variability, particularly in the Southeast Atlantic. In-depth analysis of upper-ocean heat content reveals that a significant improvement of zonal heat transport in the Southeast Atlantic leads to skillful prediction of decadal SST variability there. These results demonstrate potential roles of subsurface ocean assimilation in the skillful prediction of decadal climate variability over the South Atlantic.
Highlights
Decadal climate variability is one of key research issues for regional societies to mitigate its related damages and build long-term adaptation plans
Decadal climate variability is defined as low-frequency fluctuation from the mean state, so describing the mean state helps understand its decadal variability
An improvement of decadal climate prediction in the Southeast Atlantic is demonstrated by initializing the subsurface ocean in a coupled general circulation model (CGCM) with a 3DVAR data assimilation scheme
Summary
Decadal climate variability is one of key research issues for regional societies to mitigate its related damages and build long-term adaptation plans. As a key driver of the decadal climate variability, many studies have elaborated on understanding and predicting the decadal SST variability in the tropics[1,2,3,4], the North Pacific[5,6] and the North Atlantic[7,8,9] where long-term observation data are available. Performing long-term simulation with a coupled general circulation model (CGCM), a subsequent study[12] suggested that the South Atlantic may exhibit multi-decadal variability with 25–30 year period as well. This involves variations in southward extension of the subtropical high, which results in modulating meridional heat transport and generating SST variability in the South Atlantic. Relative roles of surface and subsurface ocean initializations in the decadal climate predictions are examined
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