Role of subsurface ocean in decadal climate predictability over the South Atlantic

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.

Impact of initialization methods on the predictive skill in NorCPM: an Arctic–Atlantic case study

“…Since then, many procedures and techniques have been developed to deal with inherent initialization problems such as initial "shocks", model drift, and a growing variety of assimilated data. Developments range from the primary initialization of the surface ocean component to additional initialization of the subsurface ocean and other components of the climate system (Morioka et al 2018); from updates of single model components (Weakly-Coupled DA) to cross-component updates during DA in particular model components (which we denote here as Strongly-Coupled DA) (Penny et al 2019) are current aspects under development and investigation.…”