Various numerical models, such as that of Gent and Cane (see, e. g., Murtugudde et al. 1996) and the LODYC model (Delecluse et al. 1993) have correctly reproduced the eastward movement of the pool (see e. g., Picaut et al. 1996 and the references mentioned therein). To aid in the interpretation of results from complicated models of this type, and of observations, it is helpful to use analytical results based on idealized models with simplified physics and geometry.

Fig. 1.

Left panel: Sea surface temperature (SST) in the tropical Pacific during June-July-August 1987 (EI Nino). Contour interval is 1℃, except for the 28.5 and 29.5℃ isotherms. SST warmer than 29℃ is shaded. The western shaded region is the warm pool under discussion. (Reproduced from Picaut and Delcroix 1995.)

Right panel: Top view of the idealized (modelled) pool; (ρ-Δρ₁) is the density of the pool and ρ is the density of the water ahead of and below the pool. This slightly heavier water will be referred to as the much deeper water which is “intermediate water” even though it has no relationship to what is usually called “intermediate water”. The “wiggly” arrow indicates migration.

Fig. 2.

Left panel: Density (σ_t) along the equator in January-February 1990 (no El Nino) showing the vertical structure of the pool and the water underneath it. CTD stations are indicated by small triangles at the bottom. Contours are at intervals of 1kg m^-3 (density). Shading indicates densities less than 22kg m^-3 (the warm pool) and hatching indicates water heavier than 25kg m^-3 (deep water). Note that the light pool (density less than 22kg m^-3) is associated with both warm water (temperature greater than 29.0℃) and low salinity (＜ 35%) water. (Adapted from Kuroda and McPhaden 1993.)

Right panel: Idealized side view of the pool. The "barrier layer separates the light pool on top from the deep water underneath.It consists of intermediate water forced to dive under the pool (as the pool propagates eastward) and, consequently, will be sometimes referred to as "intermediate water" (see related footnote in text). Solid arrows show the velocity field (viewed from a fixed coordinate system).

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