Tropical internal atmospheric variability and ENSO
예상욱; Ben P Kirtman
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 model (CGCM). 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 grid point. In an idealized 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 suggests that tropical internal atmospheric variability contributes to a strengthening and broadening of the interannual-to-decadal timescales of tropical Pacific SSTA variability . However, the internal dynamics noise plays different roles in its effect on the interannual and decadal SSTA variability in the tropical Pacific. The tropical atmospheric internal variability is largely serving to modify 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.