Relative importance of the processes contributing to the development of SST anomalies in the eastern pole of the Indian Ocean Dipole and its implication for predictability
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Using outputs from an ocean general circulation model, the relative importance of the processes contributing to the development of the Indian Ocean Dipole (IOD) is examined systematically based on two metrics. One metric quantifies the relative importance of the surface heat flux term against the oceanic terms, while the other metric compares the contribution from the horizontal advection and vertical diabatic terms. It is revealed that the anomalous cooling in the eastern tropical Indian Ocean associated with the positive IOD varies with events and four representative events are investigated in more detail. During the 1991 IOD, the horizontal advection term made the largest contribution to the eastern cooling, and the vertical diabatic term was equally important in the early stage of the development. In the 1994 event, negative SST anomalies were generated by the surface heat flux term at first, and then matured by the vertical diabatic term. Anomalous cooling during the 1997 IOD was mainly produced by the vertical diabatic term. In 2012, anomalous surface heat flux and horizontal advection played the crucial role in the development of the eastern pole, but the vertical diabatic term opposed to the anomalous cooling. Furthermore, the dependence of the seasonal prediction skill by a global ocean–atmosphere coupled general circulation model on the generation mechanisms was examined. It is demonstrated that events with the vertical diabatic term playing a more important role in the development of the eastern pole are better predicted than those with the vertical diabatic term making relatively small contribution or opposing the occurrence.
KeywordsIndian Ocean Dipole Mixed-layer heat balance Seasonal prediction Metric Ocean general circulation model Coupled general circulation model
We thank two anonymous reviewers for their constructive and insightful comments. The present research was supported by the Japan Society for Promotion of Science through Grant-in-Aid for Scientific Research (B) 16H04047 for T. T. and Grant-in-Aid for Young Scientists (B) 16K17810 for T. D. Also, the present research was partly carried out for the iDEWS project supported by SATREPS Program of JICA/AMED in Japan and ACCESS (NRF/DST) in South Africa, and the Environment Research and Technology Development Fund (2-1405) of the Ministry of the Environment, Japan. The OGCM was run on SR16000 system of the Information Technology Center, the University of Tokyo under the cooperative research with Atmosphere and Ocean Research Institute, the University of Tokyo. The SINTEX-F1 seasonal climate prediction was conducted on the Earth Simulator at JAMSTEC. We are grateful to Drs. Jing-Jia Luo, Sebastian Masson, and our European colleagues of INGV/CMCC, L’OCEAN, and MPI for their contribution to developing the prototype of the systems.
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