Interannual Volume Changes and Heat Transport Pathways in the Tropical Pacific

Previous observational and numerical modeling studies have arrived at contradictory conclusions about mass and heat transport, particularly meridional transport, in the tropical Pacific during El Niño events. The present study uses TOPEX/Poseidon altimetric heights and a sigma-coordinate model to asses tropical Pacific volume changes during El Niño. We have previously presented results concerning the large-scale pattern of El Niño related volume redistribution, in which we showed that volume is indeed lost from the tropics during events, although this loss is smaller than the redistribution within the tropics. The volume redistribution was shown to be dominated by transports of heat. Recently, we have used Lagrangian techniques to examine the specific three dimensional pathways of heat transport through an El Niño event. The redistribution of heat, and therefore volume, occurs both along the equator and through interior pathways in both hemispheres. These interior pathways are anomalously strong and shallow during El Niño, bringing warm water into the eastern equatorial Pacific. Anomalous upwelling is an important factor in the cold anomalies in the western near-equatorial Pacific during El Niño. Similarly, anomalous downwelling leads to off-equatorial warm anomalies along the coasts of North and South America, and to anomalies near 20° S and 20° N.