East Asia and Western Pacific METEOROLOGY AND CLIMATE

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On ENSO time scales, the perturbed atmospheric
circulation drives changes in the sea surface
temperature in the Atlantic and the Indian Oceans.
While these changes are locally very significant,
they generally follow the Pacific variability and
are smaller in magnitude.
Two families of theories (instability and quasicyclic
equilibrium) of variability on the ENSO time
scale have emerged, both depend on the character of
the coupled system.
Several climate models have been developed and
model-based climate forecasts are being made.
These models are routinely initialized by data from
the TOGA monitoring program. Despite the
substantial progress gained through the TOGA
program, there is still considerable doubt
regarding which elementary physical processes
maintain the mean and transient state of the warm
pool regions of the western Pacific Ocean.
Processes and thought which need further study are:
- Atmospheric response in models has been shown to be
extremely sensitive to SST variations, especially when
the SST is warm. However, model assessments of ocean
structure almost universally predict temperatures which
are far too warm although the reason for these
discrepancies is not understood. Presumably, the
discrepancies are associated with poor assessments of
heat, momentum and water fluxes between the ocean and
atmosphere;
- The heat balance of the warm pool region of the
western Pacific Ocean is only known approximately with
discrepancies of the order of 80 win . The relative
involvement of the slowly evolving atmospheric flow
(such as the trade wind regime) or the higher
frequency, more episodic, equatorial events (such as
westerly bursts and organized convective phenomena) are
not understood;
- Theories of ENSO require the instability of, or
the oscillation about, the basic state of the
coupled system. Yet, the maintenance of that
basic state and why the temperature of the warm
pool lies between 28° and 30° C with a broad,
low gradient character is not well understood.