HR: 1300h
AN: OS52D-02    [PDF]
TI: Interannual Variability in the Tropical Atlantic From an Intermediate Coupled Model
AU: * Illig, S
EM: illig@notos.cst.cnes.fr
AF: LEGOS, 14, av E. Belin, Toulouse, 31400 France, Metropolitan
AU: Dewitte, B
EM: dewitte@ird.noumea.nc
AF: IRD NOUMEA, BP A5, Noumea, 98848 New Caledonia
AU: Ayoub, N
EM: ayoub@notos.cst.cnes.fr
AF: LEGOS, 14, av E. Belin, Toulouse, 31400 France, Metropolitan
AB: The modes of variability that regulate the climate in the tropical Atlantic at interannual and decadal time scales are an inter-hemispheric SST mode often referred as the Atlantic dipole and a zonal equatorial mode, similar to the Pacific ENSO mode. Using a linear model forced with different wind stress products (ECMWF, ERS, FSU), the dynamics of the so-called Atlantic El Ni¤o mode, is shown to share many characteristics with those of the Pacific ENSO mode, with Kelvin and Rossby waves of the first three baroclinic modes contributing to a large extent of the SST variability (72\%* in the ATL3 ([20$\deg$W-0$\deg$E ; 3$\deg$S-3$\deg$N]) region) through zonal and vertical advection. The linear ocean model is then coupled to the Neelin\&Zeng Quasi-Equilibrium Tropical Circulation Atmospheric Model (QTCM). The mixed layer (ML) component is similar to the Zebiak\&Cane(1987)'s model but uses a different mean state and parameterization for subsurface temperature. We investigate how this intermediate coupled model (ICM) is able to sustain oscillations at interannual time scales, within a certain parameter range. Sensitivity tests to the coupling efficiency are carried out, in order to examine the transition from the uncoupled mode (weak-coupling limit) to the coupled mixed modes (strong-coupling limit). The role of zonal advection (zonal current anomaly) versus vertical advection (thermocline depth anomaly) in setting of characteristics of the coupled instabilities is investigated. The objective is to see whether, like in the tropical Pacific, the timescales of the variability are controlled by the relative contribution of zonal and vertical advections. The effect of remote forcing originating from the Pacific ENSO is also studied. As suggested by Zebiak (1993), the Pacific ENSO remote forcing can act as an excitatory of the Tropical Atlantic instabilities. Depending on the season, it can also trigger the equatorial Atlantic warmings. * Ratio of the Reynolds SST anomalies variability and the model SST anomalies variability forced by ERS winds (1992-2000).
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 4215 Climate and interannual variability (3309)
DE: 4231 Equatorial oceanography
DE: 4255 Numerical modeling
DE: 9325 Atlantic Ocean
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting