Tropical climate variations such as El Nino/Southern Oscillation (ENSO) and ENSO Modoki in the tropical Pacific and the Indian Ocean Dipole Mode (IOD) have enormous impacts on the global climate and the human societies. Therefore, there is a significant benefit to our societies if these climate events are predicted sufficiently ahead of their occurrences. Since the mid-1980s, many research institutes and operational centers have developed various numerical prediction models for ENSO forecast. Also, the IOD and ENSO Modoki predictions are attempted by some of the leading modeling groups recently.
The numerical prediction of weather has been proven to be very useful to us now days because of the superb advancements made in that area of research during last several decades. Such weather forecast systems mostly employ standalone atmospheric models on the assumption that the oceans do not change in the relatively short prediction period (~1 week). However, such standalone atmospheric models are not ideal for predictions of climate phenomena like ENSO, ENSO Modoki and IOD that strongly depend on the ocean-atmosphere interactions. Application of ocean-atmosphere coupled model is naturally a proven approach to overcome the shortcoming of the standalone atmospheric model and to realistically simulate the climate phenomena.
For our climate predictions, we have developed the SINTEX-F1 ocean-atmosphere coupled general circulation model under the EU-Japan research collaboration. Based on this seasonal prediction system, we have performed climate predictions at least 1 year ahead and distributed the prediction information on JAMSTEC website since 2005. We have achieved great successes in these years and SINTEX-F1 has become one of the leading models of the world for predicting the tropical climate variations in particular the IOD, the ENSO and the ENSO Modoki.
We adopt the SINTEX-F1 atmosphere-ocean coupled general circulation model, which was developed under the European Union-Japan research collaboration. The SINTEX-F1 consists of the atmospheric component ECHAM4 and the ocean component OPA8. The ECHAM4 has the horizontal resolution of T106 (~100km) with 19 vertical levels. The OPA8 has the resolution of 2° Mercator mesh (enhanced to 0.5° in the latitudinal direction near the equator) with 31 vertical levels. The atmosphere and ocean components in the model interact every 2 hours via OASIS2 coupler without any flux corrections.
Since atmosphere-ocean coupled system involves the strong nonlinearity, variations in initial conditions and physical schemes lead to diverse solutions. Therefore, as is customary now, we employ many ensemble members to reduce the prediction uncertainties associated with different initial conditions and physical schemes. For creating ensemble members based on initial conditions in our prediction system, model sea surface temperature is nudged toward three different observed sea surface temperatures besides three different negative feedback values to the surface heat flux. In addition, three different atmosphere-ocean coupling schemes are employed to represent other ensemble members. Through this processes, in total 27 ensemble members are employed for our seasonal to interannual climate predictions initiated every month.