a Coupled Atmosphere-Ocean Model in the Tropics with Various Climatological Backgrounds
A tropical atmosphere-ocean coupled model is used to study the effects of a zonally sloping thermocline on the coupled oscillatory modes in the tropics. A two and one half layer oceanic model is coupled with the steady state Gill's atmospheric model. A constant depth mixed layer is included in the upper layer. The SST is calculated in the mixed layer. The interface of the two upper layers is sloping and prescribed as the observed 20^ circC isotherm in the Pacific Ocean. The formula of Seager et al. (1988) is used to compute the entrained water temperature. The unstable waves behave like the propagating modes with much larger SST anomalies observed in the eastern Pacific Ocean. It is found that the coupled instabilities are very sensitive to the steepness of the tilted thermocline in the central Pacific Ocean. A series of numerical experiments have been performed, with different thermocline profiles, in the Pacific Ocean. An interannual oscillation is self sustained when a realistic thermocline profile is specified. The initial disturbance slowly decays and comes back to the equilibrium state of rest when the thermocline slope becomes steeper. The oscillation amplitude becomes much larger when a flatter thermocline is used. An additional numerical experiment is conducted to investigate the role of the western boundary reflection. It is found that the reflection does not change the oscillatory period although it affects the amplitude. A simpler conceptual model is also used to explain the physics.
- Pub Date:
- PACIFIC OCEAN;
- EL NINO;
- Physical Oceanography; Physics: Atmospheric Science