Understanding the influence of tropical intraseasonal oscillation in predicting the Indian Ocean Dipole

Abstract Indian Ocean Dipole (IOD) is an important source of seasonal-interannual predictability, while its prediction is a long-standing challenge, which is partially affected by tropical intraseasonal oscillation (ISO). This study revisits the influence of ISO on the evolution of IOD. Furthermore, the impact of intraseasonal signals on the IOD prediction is investigated using an atmosphere-ocean coupled model. Compared to the prediction initialized with a pure SST-nudging (NOATM), the prediction skill of IOD at lead times of 1-6 months is improved when initialized with a combination of SST-nudging and atmospheric nudging (NDJRA). This improvement may benefit from a realistic initial condition and prediction in the first month for tropical ISO such as the boreal summer intraseasonal oscillation (BSISO) and its associated easterly/westerly events (E/WWEs). As seen in the observation and predictions, the frequency of active BSISO in summer is significantly correlated to the sea surface temperature (SST) anomalies over the eastern Indian Ocean (EIO) in autumn, and the WWEs in summer excite downwelling Kelvin waves and accumulate heat in the subsurface of the EIO. However, the effect of additional atmospheric nudging varies when predicting different IOD events. For instance, it improves the prediction of pIOD in 1997 while degrades the prediction of pIOD in 2006, which is attributed to the asymmetrical relationship between intraseasonal easterly/westerly wind and SST in the EIO. Our results reinforce the importance of high-frequency signals in the IOD prediction. The limited skill in predicting ISO and the across-time-scale interactions may restrict the model’s capability in predicting the IOD.