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Findings on Earth

For the first time, scientists have demonstrated with precise measurements that Earth’s changing gravity field can effectively monitor changes in the planet’s climate and weather. This finding comes from more than a year’s worth of data from the Gravity Recovery and Climate Experiment (GRACE). GRACE is a two-spacecraft, joint partnership of NASA and the German Aerospace Center.

Published results show that monthly changes in the distribution of water and ice masses could be estimated by measuring changes in Earth’s gravity field. The GRACE data measured the weight of up to 10 centimeters (four inches) of groundwater accumulations from heavy tropical rains, particularly in the Amazon basin and Southeast Asia. Smaller signals caused by changes in ocean circulation were also visible. Launched in March 2002, GRACE tracks changes in Earth’s gravity field. GRACE senses minute variations in gravitational pull from local changes in Earth’s mass.

To do this, GRACE measures, to one-hundredth the width of a human hair, changes in the separation of two identical spacecraft in the same orbit approximately 220 kilometers (137 miles) apart. GRACE maps these variations from month to month, following changes imposed by the seasons, weather patterns and short- term climate change. Understanding how Earth’s mass varies over time is an important component necessary to study changes in global sea level, polar ice mass, deep ocean currents, depletion and recharge of continental aquifers. GRACE monthly maps are up to 100 times more accurate than existing ones, substantially improving the accuracy of many techniques used by oceanographers, hydrologists, glaciologists, geologists and other scientists to study phenomena that influence climate.