Woods Hole Oceanographic Institution




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Gravity Recovery and Climate Experiment

GRACE, twin satellites launched in March 2002, are making detailed measurements of Earth's gravity field which will lead to discoveries about gravity and Earth's natural systems. These discoveries could have far-reaching benefits to society and the world's population.

Ocean currents transport mass and heat between different regions of the Earth. Knowledge of these currents is therefore vitally important for Earth climate sciences. Some of the more familiar currents include the Gulf Stream off the eastern seaboard of the USA, the Kuroshio Current in the western Pacific off the coast of Japan; the Antarctic Circumpolar Current (ACC), which is the only current to travel through all major ocean basins; and the Equatorial Currents.

Historically, knowledge of these currents has come from measurements from very limited number of current meters or drifter buoys (which measure the current directly at selected points in the oceans), or indirectly from the knowledge of slopes of the dynamic ocean topography. The dynamic ocean topography, and thus the currents, can be computed in two ways: 1) from measurements through the ocean depth of temperature and salinity, using instruments dropped from ships or from moored buoys, or 2) the difference between sea surface height measured by satellite altimeters and a geoid model from GRACE. This independent knowledge of absolute surface currents from altimetry and GRACE can now be used in combination with the temperature and salintiy profiles to extract the currents as a function of depth. This in turn will improve our knowledge of mass and heat transported by these current systems.

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