Idealized ENSO Simulation
In the ocean, large-scale wave-like motions play a large role in ENSO (El
Niño - Southern Oscillation). In this figure we see a perspective view
of the entire Tropical Pacific Ocean. The animation follows the evolution of
sea level (the undulating surface) and sea-surface temperature (color) for a
Warm event followed by a Cold event as simulated by the numerical model of
Battisti(1988). This model is a version of the Zebiak-Cane model, one of the
first coupled atmosphere-ocean models used to make predictions of ENSO.
Motions in the real world are significantly more complex than those shown here.
The relatively small motions in sea level shown here (10 - 20 centimeters) are
indicative of much larger motions in the opposite direction in the depth of
the thermocline below the surface. (Thermocline
animation) Vertical displacements of the thermocline are particularly
important along the equator in the eastern half of the Pacific basin, where
they control the availability of cold water that can reach the surface through
the process known as upwelling. For example, when the sea level is low, the
thermocline tends to be shallow, indicating that unusually cold water is near
the surface. Upwelling motions can then bring this cold water to the surface,
resulting in cold conditions. When the sea level is high the situation is
reversed, with cold water lying too deep to reach the surface. The result is a
The waves on the thermocline are caused by winds blowing over the ocean, and
they can freely propagate for some time before they die out. The reflections
of the waves off the western boundary are an important process in the
delayed-oscillator theory for ENSO.
Animations of Observed SST and Thermocline 1995- 1998
Once you get the image, reload to repeat the animation.
Note that the label "Sea Level anomaly" in these plots is
incorrect. We show only SST and 20C Isotherm depth.
TOGA TAO Anomalous SST and 20C Isotherm Depth (7 MB)
NCEP Ocean Analysis Anomalous SST and 20C Isotherm
Depth (7 MB)