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 warm event.

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)

Joe Barsugli