Mid-latitude source of the ENSO-spread in SINTEX-F ensemble predictions
- 88 Downloads
The ensemble spread of seasonal prediction is investigated in this study to understand its role in the predictability of El Niño/Southern Oscillation (ENSO) based on the results of SINTEX-F2, a coupled ocean–atmosphere general circulation model. In the SINTEX-F2 seasonal prediction system, the first ENSO precursor appears as a cyclonic wind anomaly over the central north Pacific in boreal winter (January). This is followed by warm SST, positive rainfall and cross-equatorial southerly wind anomalies in the northern hemisphere during spring (particularly in April). These anomalies in April are accompanied by westerly wind anomaly in the western equatorial Pacific. Finally, El Niño-like conditions with warm SST and positive rainfall anomalies become dominant in the ensemble standard deviation after boreal summer. The 500 hPa geopotential height suggests that stochastic atmospheric variability excites El Niño-like spread through air-sea interaction. The oceanic response in the form of upper heat content (in the top 150 m) appears to result from the equatorial wind forcing during boreal spring and summer. These model results suggest that air-sea interaction related to the seasonal footprinting mechanism (SFM) is important for ENSO spread and the “spring predictability barrier”. The dependence of ENSO spread on the background ensemble-mean state is also investigated.
KeywordsENSO Seasonal prediction Ensemble spread
The authors would like to appreciate careful reading and constructive comments by Drs. Masami Nonaka, Bunmei Taguchi and Ingo Richter. Numerical experiments of SINTEX-F2 were executed on the Earth Simulator of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We are grateful to Drs. Wataru Sasaki, Jing-Jia Luo, Sebastian Masson, Andrea Storto, and our European colleagues of INGV/CMCC, L’OCEAN, and MPI for their contribution to developing the prototype of the systems. This research was supported by the Environment Research and Technology Development Fund (2–1405) of the Ministry of the Environment, Japan, the Japan Agency for Medical Research and Development (AMED) and Japan International Cooperation Agency (JICA) through the Science and Technology Research Partnership for Sustainable Development (SATREPS) project for iDEWS South Africa, and JSPS KAKENHI Grant Number 16H04047 and 16K17810.
- Madec G (2008) NEMO ocean engine, version 3.0. Note du Pôle de modélisation de l’Institut Pierre-Simon Laplace, vol 27. Institut Pierre-Simon Laplace, France, 209 (ISSN 1288–1619)Google Scholar
- Roeckner E et al (2003) The atmospheric general circulation model ECHAM5. Part I: Model description. MPI-Rep. 349. Max-Planck-Institut für Meteorologie, Hamburg, pp 140. https://www.mpimet.mpg.de/fileadmin/publikationen/Reports/max_scirep_349.pdf. Accessed 30 May 2018
- Vecchi GA, Harrison DE (2003) On the termination of the 2002–03 El Niño event. Geophys Res Lett 30(18)Google Scholar