Predictability of Indian Ocean precipitation and its North Atlantic teleconnections during early winter

The Tropical Western-Central Indian Ocean (WCIO) precipitation anomalies play an important role in modulating the anomalous climate conditions in the North Atlantic and European (NAE) region during the early boreal winter (November-December; ND) season. In this study, we analyzed the forcing mechanism and predictability for the early winter tropical WCIO precipitation anomalies and its teleconnections to the North Atlantic region. The two main forcing mechanisms emerging are the autumn Indian Ocean Dipole (IOD) and a direct atmospheric teleconnection from El Nino-Southern Oscillation (ENSO). Since the autumn IOD is partially forced by ENSO, their independent contributions are also investigated. We found the IOD dominates over the ENSO contribution. The ECMWF-SEAS5 seasonal re-forecast reproduces these forcing mechanisms well and shows a substantial prediction skill for early winter WCIO precipitation. Moreover, the North Atlantic response to the positive WCIO phase projects spatially onto the positive North Atlantic Oscillation (NAO) phase through atmospheric teleconnections and leads to warming in central and western Europe. This teleconnection is reproduced by ECMWF-SEAS5, but with weaker amplitude. Moreover, a significant prediction skill for the NAO as well as for the central and western European temperature anomalies is noted, which is mostly induced by the Indian Ocean precipitation anomalies during early winter.

Automated summary

This study finds that the autumn Indian Ocean Dipole (IOD) and El Nino-Southern Oscillation (ENSO) are the two main forcing mechanisms for the early winter tropical Western-Central Indian Ocean (WCIO) precipitation anomalies. The IOD dominates over the ENSO contribution. Furthermore, the Indian Ocean precipitation anomalies during early winter also significantly affect the North Atlantic Oscillation (NAO) and the temperature anomalies in central and western Europe.