Advanced ENSO Theory: The Delayed Oscillator
The Simplified Tropical Pacific Ocean
Consider the simplified representation of the tropical Pacific Ocean
shown in Figure 1. The ocean areas are shaded in blue in this figure while
the land areas are shaded in gold. The western-most and eastern-most points
in the model are solid walls, as are the two idealized land masses (representing
Australia and Indonesia in the west, and Central and South America in the
Figure 1. Idealized Pacific Ocean basin
The ocean temperature is assumed to vary only with depth, with the
depth dependence representing an idealized thermocline structure -- that
is, a region of rapidly decreasing temperature with depth that separates
the warmer near-surface ocean from the colder deep ocean. With no horizontal
variations of temperature (or salinity), there are also no horizontal variations
in density, and hence pressure (there is a balance in the vertical between
changes in pressure and the force of gravity, dependent only on density).
Absence of horizontal pressure variations in turn implies that there are
no mean currents.
Under these assumptions, which represent a fair first-order approximation
to the real time-mean tropical oceans, it becomes straightforward to trace
the evolution of disturbances, and isolate key processes associated with
the delayed oscillator theory.