- TOPEX/Poseidon (satellite) was developed to measure the ocean's
sea-surface height. By knowing the sea-surface height, scientists are able to
develop very accurate maps of ocean currents and sea-surface heights
related to heat content.
- TOPEX/Poseidon and its follow-up satellite--Jason--are the result
of a joint program between the U. S. and French space agencies.
- Satellites, such as TOPEX/Poseidon, give scientists early clues to
an El Niño or La Niña event. By examining the satellite
images, sea-surface height maps give scientists an almost biweekly
look at the ocean and its changes. It is actually the sea-surface
height anomally that scientists use to detect events that can lead
to El Niño or La Niña.
Variations in Atmospheric Pressure
- As the warm water in the tropical Pacific shifts along the equator,
the areas of high pressure and low pressure shift as well. Just a
slightly lowered atmospheric pressure can cause a change in the
- An index, known as the Southern Oscillation Index, is used to compare
the barometric pressure in Tahiti and Darwin, Australia. During a
normal year, the index is zero. During an El Niño, the index
will be a negative number because the pressure in Australia is higher
than in Tahiti. This causes the trade-winds to weaken or even reverse
(westerly wind burst).
- Changes in the wind field can also be used to determine when El Niño
conditions are beginning or to judge the severity of the current El
- To provide important data, NOAA operates a network of buoys which
measure temperature, currents, and winds in the equatorial band. These
buoys daily transmit data which are available to researchers and forecasters
around the world in real time.
- The TAO (Tropical Atmosphere Ocean) array consists of approximately
70 ATLAS and current meter moorings in the tropical Pacific Ocean,
telemetering oceanographic and meteorological data in real time via
the Argos satellite system. Designed to improve detection, understanding,
and prediction of El Niño, TAO is a major component of the
global climate observing system. The array is presently supported
by an international consortium, involving cooperation between the
United States, France, Japan, and Taiwan.
- Measurements from buoys and ships describe the bulk temperature of
the ocean several meters below the surface.