TOPEX/POSEIDON Satellite Data for El Niño
Helping predict future El Niño events

TOPEX/POSEIDON's orbit is measured precisely by using two ground-based systems plus a Global Positioning System (GPS) tracking system.  The satellite's altimeter bounces radar signals off the surface to determine sea-level height. Gravity's influence on the shape of the ocean is subtracted from the data to obtain the ocean topography created by currents.

In a normal year, the strong trade winds to the west push warm surface water against the western boundary of the Pacific Ocean near Australia and Indonesia, while nutrient rich cold water wells up along the west coast of South America, helping fish thrive. TOPEX/POSEIDON has tracked this building up of warm water in the western Pacific Ocean, which can be as much as 1 meter higher than the eastern Pacific.

The trade winds are controlled by an air/sea interaction in which SST (Sea Surface Temperature) plays a huge part. In an El Niño year, these trade winds weaken causing upwelling to decrease which in turn suppresses the upwelling of cold water. Thus, the thermocline deepens as a result of the Kelvin and Rossby Waves.

All of this has been measured by TOPEX/POSEIDON during El Niño events since 1992.   The image at the bottom is an actual image of TOPEX/POSEIDON satellite data.  The image on top is a computer simulation.    These both represent images taken during December 1994. 

The colors show the sea level relative to a two-year mean (average) over 1993-1994.    The color magenta indicates 15 centimeters lower, and red 15 centimeters higher, than average.  El Niño caused the excessive heat associated with the high sea levels (red and yellow) in the central equatorial Pacific Ocean.  The associated rise of tropical air and formation of rain clouds contributed to the severe weather and heavy reains in California during winter 1995. 

Thus, the top image would be used in dynamical forecasts whereas the image on the bottom would be used for statistical forecasts. 

This comparision shows that the model underestimated the magnitude of oceanic features during an El Niño event. 

Using TOPEX/POSEIDON data, scientists are working to improve the performance of such models, with the goal of reliably predicting climatic many events, not just the dreaded El Niño.