Contribution of ENSO related oceanic teleconnection to asymmetry of the Ningaloo Nino/Nina

Hidehiro Kusunoki, The University of Tokyo, Department of Earth and Planetary Science, Graduate School of Science, Tokyo, Japan, Shoichiro Kido, The University of Tokyo, Department of Earth and Planetary Science, Graduate School of Science, the University of Tokyo, Tokyo, Japan and Tomoki Tozuka, The University of Tokyo, Tokyo, Japan
Abstract:
Ningaloo Nino/Nina is the dominant mode of interannual variability of sea surface temperature (SST) in the southeastern Indian Ocean. Considering its large impacts on the local marine ecosystem and precipitation, better understanding of its mechanism and predictability is desirable. According to previous studies, both local air-sea interaction and remote forcing contribute to generation and amplification of the Ningaloo Nino/Nina. The latter forcing includes the atmospheric teleconnection and oceanic wave propagation through the Indonesian archipelago, mainly associated with the El Nino/Southern Oscillation (ENSO). One of the important characteristics of the Ningaloo Nino/Nina is their asymmetry; the Ningaloo Nino is stronger than the Ningaloo Nina. This suggests the presence of some asymmetry in these processes. However, no studies to date focused on this topic.

Using a regional ocean modeling system (ROMS), the impact of oceanic wave propagation on the amplitude and asymmetry of SST anomalies associated with the Ningaloo Nino/Nina is investigated. For these purposes, a sensitivity experiment in which oceanic lateral boundary conditions are replaced by the monthly climatology is conducted. The results of composite and heat budget analyses suggest that downwelling (upwelling) Kelvin waves from the western tropical Pacific associated with La Nina (El Nino) that often co-occur with the Ningaloo Nino (Nina) are stronger (weaker) and contribute to the asymmetry.

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