1:45 PM - 2:00 PM
[ACG33-01] A study on impacts of interbasin coupling strength on climate modes in the tropical Indian and Pacific Oceans using linear inverse models
Keywords:Tropical interbasin interactions, linear inverse model, air-sea interactions, El Niño-Southern Oscillation, Indian Ocean Dipole
The tropical basin interaction (TBI) has a strong impact on the evolution of sea surface temperature (SST) in the tropics, in which air-sea interaction also plays an important role. In this study, the impacts of TBI and air-sea interaction on climate modes in the tropical Indian Ocean (IO) and Pacific Ocean (PO) are assessed with a linear inverse model (LIM) framework built based on SST and 10 m zonal wind (u10) anomalies in the tropical IO and PO. The magnitudes of TBI and air-sea interaction are adjusted for the first time by gradually [Microsof1] changing the values of linear operators in LIMs.
First, the effects of TBI are investigated in stochastically-forced LIM simulations with different interbasin coupling strengths. The amplitude of the El Niño-Southern Oscillation (ENSO) increases as the TBI becomes weaker, indicating the delayed negative feedback of the IO on the ENSO. On the other hand, the Indian Ocean Dipole (IOD) variability is reduced as the TBI is weakened, but the IOD exists even when the PO and IO are completely decoupled, supporting that the IOD is an inherent climate mode in the IO. In addition, the peak of the IOD shifts two months earlier when completely decoupled, suggesting that the TBI affects the seasonality of the IOD. It is found that reduced TBI results in larger low-frequency variability of ENSO, while reinforced TBI leads to a large increase in the biennial components of both ENSO and IOD. By adjusting the corresponding parts in the linear operators, the influence of air-sea coupling strength is also examined. It is shown that air-sea interactions promote SST variability in both the IO and PO, which is expected from the importance of the positive Bjerknes feedback in the tropics. The air-sea interaction is also found to play an important role in the collapse of the eastern pole of the IOD. Moreover, the seasonality is also enhanced as the air-sea coupling strength is enhanced.
First, the effects of TBI are investigated in stochastically-forced LIM simulations with different interbasin coupling strengths. The amplitude of the El Niño-Southern Oscillation (ENSO) increases as the TBI becomes weaker, indicating the delayed negative feedback of the IO on the ENSO. On the other hand, the Indian Ocean Dipole (IOD) variability is reduced as the TBI is weakened, but the IOD exists even when the PO and IO are completely decoupled, supporting that the IOD is an inherent climate mode in the IO. In addition, the peak of the IOD shifts two months earlier when completely decoupled, suggesting that the TBI affects the seasonality of the IOD. It is found that reduced TBI results in larger low-frequency variability of ENSO, while reinforced TBI leads to a large increase in the biennial components of both ENSO and IOD. By adjusting the corresponding parts in the linear operators, the influence of air-sea coupling strength is also examined. It is shown that air-sea interactions promote SST variability in both the IO and PO, which is expected from the importance of the positive Bjerknes feedback in the tropics. The air-sea interaction is also found to play an important role in the collapse of the eastern pole of the IOD. Moreover, the seasonality is also enhanced as the air-sea coupling strength is enhanced.