Observed characteristics at the eastern edge of the warm pool in the western Pacific Ocean

C. Maes, K. Ando, T. Delcroix, W. S. Kessler, M. J. McPhaden, and D. Roemmich
Contact: Christophe.Maes@ird.fr

The western Pacific warm pool is of fundamental importance to interannual variations associated with El Niño and the Southern Oscillation (ENSO), the strongest year-to-year climate variation on the planet. The warm pool encompasses the highest mean sea surface temperatures (SSTs) in the world ocean, intense atmospheric deep convection and heavy rainfall, and the formation of thick salt-stratified barrier layers that help to sustain the high SSTs. In order to evaluate the importance of salinity variations in such dynamical relationships, three different sources of sea surface salinity (SSS) observation are jointly analyzed along with the SST, surface zonal current, rainfall and surface zonal wind. The features of the upper ocean layers are derived from the vertical profiles provided by Argo floats. At the surface, a salinity front of the order of 0.4 over 1-2° in longitude and a barrier layer of O(20m) thickness are persistent features during the period 2002-2004. This result contrasts with that based on historical data analyses which indicate an average SSS gradient of 0.4 over 10-15° in longitude. The analysis also reveals a tighter empirical relationship than previously observed between the eastern edge of the warm pool, high SSTs, the presence of barrier layers, and the fetch of westerly wind bursts. Our results suggest that the eastern edge of the warm pool is a critical in controlling ocean-atmosphere interactions in the western Pacific and highlight the importance of the upper ocean salinity in climate variability.