The characteristic oscillation induced by coupled processes between oceanic vertical modes and atmospheric modes in the tropical Pacific.
Sang-wook Yeh, Boris Dewitte, Jong-Ghap Jhun and In-Sik Kang
An intermediate coupled model (ICM) based on an ocean model with three vertical modes and a statistical atmosphere model was used to investigate the relationship between the dominant modes of variability in the ocean and the atmosphere in the Tropical Pacific. Tests on sensitivity to the oceanic vertical structure of the ocean show that the time scale of variability in the sea surface temperature anomaly (SSTA) mainly depends on the relative contribution of the baroclinic modes. The first two atmospheric modes, i.e. the central and off-equatorial modes, play different roles in modulating the impact of oceanic baroclinic modes on SST changes through coupled processes. In the model, the central mode excites the second oceanic mode which drives the observations-like interannual variability in the model. The atmospheric off-equatorial mode, on the other hand, favors the gravest baroclinic mode and consequently shortens the frequency of SSTA variability in the tropical Pacific. This suggests a possible mechanism governing time modulation of the El Niño events characteristics in the tropical Pacific.