Tropical internal atmospheric variability and ENSO
The interactive ensemble coupling strategy has been developed specifically to determine how noise due to internal atmosphere dynamics impacts climate variability within context of coupled general circulation models (CGCMs). In this study we investigate the impact of tropical internal atmospheric variability on the tropical SSTA variability using two CGCM simulations. In the control simulation, the interactive ensemble strategy is applied globally thereby reducing the noise at the air-sea interface at each ocean grid point. In a second CGCM simulation, the interactive ensemble strategy is applied locally in the extra-tropics only to isolate internal atmospheric variability in the tropics and to minimize its influence in the midlatitudes. The results suggest that tropical internal atmospheric variability strengthens the interannual-to-decadal tropical Pacific SSTA variability and leads to a broader spectral peak. However, the internal dynamics noise plays different roles when the interannual and decadal SSTA variability in the tropical Pacific is considered separately. The tropical atmospheric internal variability largely modifies the frequency as opposed to the amplitude of the SST variability on interannual timescales. On the other hand, tropical internal atmospheric variability is effective in forcing decadal SSTA variability, resulting in significant decrease of decadal SSTA amplitude in the central tropical Pacific in a CGCM when the noise is reduced via the interactive ensemble coupling strategy.