English Abstract A fundamental study of the nonlinear dynamics of the
Tropical Pacific climate system was performed within this project. Using
tools of dynamic systems theory and an intermediate coupled ocean-atmosphere
model, the physical mechanisms determining the time-mean state of the
Tropical Pacific and its variability on interannual time scales
(El-Nino/Southern Oscillation, ENSO) are described. Coupled processes
between ocean and atmosphere are not only responsible for the ENSO
variability, but also determine the zonal spatial structure of the mean
state (warm pool/cold tongue structure) and its equatorial asymmetry.
Within an equatorial symmetric coupled model, which allows the interaction
between the mean state and its variability, the ENSO mode is shown to be a
robust eigenmode of the coupled system, which is destabilised as coupling
strength is increased. The spatial structure of the mean state is central
to the propagation mechanism and spatial pattern of the ENSO mode, which was
shown to correspond well to the recently proposed recharge oscillator image,
In reality, the mean state also displays substantial equatorial asymmetry.
This asymmetry is important for the structure of the seasonal cycle in the
Tropical Pacific; its physical state has been investigated in a conceptual
model. A further and final study explored the impact of intra-seasonal
oscillations, atmospheric noise and the seasonal cycle on the interannual
variability of the coupled system.