HR: 16:15h
AN: OS52K-08    [PDF]
TI: Importance of the salinity barrier layer formation for the Pacific mean state and El Nino
AU: * Maes, C
EM: Christophe.Maes@cnes.fr
AF: IRD/LEGOS, 18 Avenue Belin, Toulouse, 31400 France
AU: Picaut, J
EM: Joel.Picaut@cnes.fr
AF: IRD/LEGOS, 18 Avenue Belin, Toulouse, 31400 France
AU: Belamari, S
EM: sophie.belamari@meteo.fr
AF: CNRM/METEOFRANCE, 42 Avenue Coriolis, Toulouse, 31057 France
AU: Delcroix, T
EM: Thierry.Delcroix@cnes.fr
AF: IRD/LEGOS, 18 Avenue Belin, Toulouse, 31400 France
AB: In the warm pool of the western Pacific Ocean, the salinity stratification of the surface layer induces a barrier layer (BL) that insulates the bottom of the mixed layer from the deeper and colder waters. The presence of BL thus alters the heat and momentum transfer from the atmosphere to the ocean. Recent results with a coupled model demonstrate that the destruction of BL during the onset phase or the build-up phase was responsible for the failure of simulated El Nino. In the presence of zonal and meridional salinity gradients, different processes have been suggested for generating thick and long-lived BL in the equatorial band of the warm pool. Among those, surface jets induced by westerly wind bursts (WWBs) are able to tilt the zonal gradient of the salinity into the vertical. Then, due to the presence of fresh surface waters, these jets generate a BL through the depth-dependent pressure gradient. This tilting/shearing process is assessed in a coupled simulation that reproduces realistic BL, WWBs and El Nino and it is shown to be statistically robust. This process is then cancelled over the equatorial band of the warm pool by removing the salinity contribution into the pressure gradient. The coupled model response is analyzed over a 30-year period in order to determine the reasons for El Nino amplitude to be reduced. The cancellation of the tilting/shearing process results in the annihilation of the BL, and thus to an increase of the mixed layer and a decrease of sea surface temperature. Such changes in the simulated mean state of the Pacific warm pool reduce the activity of WWBs and hence of El Nino.
DE: 4231 Equatorial oceanography
DE: 4255 Numerical modeling
DE: 4504 Air/sea interactions (0312)
DE: 4522 El Ni¤o
DE: 4572 Upper ocean processes
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting