On the dynamical mechanisms explaining the western Pacific subsurface temperature buildup leading to ENSO events
Despite steady progress in the understanding of El Niño–Southern Oscillation (ENSO) in the past decades, questions remain on the exact mechanisms explaining the heat buildup leading to the onset of El Niño (EN) events. Here we use an ensemble of ocean and atmosphere assimilation products to identify mechanisms that are consistently identified by all the data sets and that contribute to the heat buildup in the western Pacific 18 to 24 months before the onset of EN events. Meridional and eastward heat advection due to equatorward subsurface mass convergence and transport along the equatorial undercurrent are found to contribute to the subsurface warming at 170°E–150°W. In the warm pool, instead, surface horizontal convergence and downwelling motion have a leading role in subsurface warming. The picture emerging from our results highlights a sharp dynamical transition at 170°E near the level of the thermocline.
Additional Information© 2015 American Geophysical Union. Received 2 MAR 2015; Accepted 18 MAR 2015; Accepted article online 24 MAR 2015; Published online 19 APR 2015. J.B. gratefully acknowledges funding from the European Commission through a Marie Curie International Outgoing Fellowship of the 7th Framework Programme for Research (project MEMENTO from the FP7-PEOPLE-2011-IOF call). X.R. acknowledges funding from the EUFP7 project EUPORIAS. NCEP/NCAR and GPCP data are obtained from http://www.esrl.noaa.gov, and ocean variables are from http://icdc.zmaw.de. The Editor thanks two anonymous reviewers for their assistance in evaluating this paper.
Published - grl52779.pdf
Supplemental Material - grl52779-sup-0001-supplementary.doc