TOPEX Outreach
Understanding Our Environment

Global Climate

TOPEX/POSEIDON continually maps changes in sea level due to heat storage in the ocean. The observations are valuable because changes in heat stored in the ocean affects our global climate. This information can help scientists predict climate changes, and possibly help avert the ill-effects that might occur from extreme weather conditions.

The upper three meters of the ocean store the same amount of heat as does the entire atmosphere. This heat is released and reabsorbed regularly in a cycle from ocean to atmosphere and back. Since unusual patterns in the rate and size of this exchange can cause severe weather, oceanographers measure the oceans' temperature to see if they can identify and predict such patterns.

In addition to affecting the weather, changes in ocean temperature affect sea-level. Themajority of sea-level rise is due to thermal expansion. As ocean temperature rises, the waterexpands to occupy more space. The melting of polar ice has an additional but more minor effect.

In the past, scientists had to rely on tide gauges and other devices to measure change in sealevel. Now we have TOPEX/POSEIDON giving us half a million observations in just one 10-day cycle.


Tides are the natural rise and fall of sea level due to pulls of gravity between the Sun, earthand Moon. The orbit of TOPEX/POSEIDON was especially chosen to permit the satellite to measure the solar and lunar tides.

A significant accomplishment of TOPEX/POSEIDON is that data from the satellite have beenused by the Science Team to produce the most accurate global maps of tides. As a result, tides can now be predicted everywhere in the deep ocean with an accuracy of 2 centimeters.

This level of accuracy is necessary to understand many oceanic and geodetic processes: tidesare important for navigation especially in coastal regions; tides slow up the rotation of themoon around the earth, and cause the moon to keep the same face toward the earth; theweight of the tides depresses the sea floor, disrupting measurements of gravity on land; andfinally, tides change the orbits of artificial satellites, such as the Hubble Space Telescope and TOPEX/POSEIDON.

Once TOPEX/POSEIDON measurements of sea level have been corrected for the influences oftides, the data are used for the study of ocean circulation.


Eddies are swirls of water currents spun off from a main current or forced by the wind. Ocean eddies may persist from a week to as long as a year, have diameters of tens to hundreds of kilometers, and extend to great depths in the oceans. These currents play an important role in ocean circulation by transporting heat, salt and nutrients through the waters.

In the atmosphere, "weather" consists of the random fluctuation of air flow. The world'soceans have their own weather, consisting of the random fluctuation of ocean currents.Eddies may be thought of as a type of oceanic weather. They play a critical role in oceancirculation, the earth's climate, and biogeochemical systems.

Eddies also play a role in human pursuits. Some large fish like to feed near the edges of cold eddies. As eddies come and go, so do schools of fish. TOPEX/POSEIDON locates eddies and the average sea-surface height changes they cause.

Weather Changing Waves


Last Modified: Sat Jul 17, 1998