Satellites reveal differences in sea level rises

[phantom power]

According to the new results, the annual world average sea level rise is about 1 millimeter, or about 0.04 of an inch. In some areas, such as the Pacific Ocean near the equator and the waters offshore from India and north of the Amazon River, the rise is larger. In some areas, such as the east coast of the United States, the sea level has actually dropped a bit over the past decade.

The surface of the sea is a constantly shifting fabric. To achieve a truer sense of how much the sea is changing in any one place, scientists measure the strength of gravity in that place. Measuring gravity over a patch of ocean or dry land provides an estimate of how much mass lies in that region. The measured mass depends on the presence of such things as mountains, glaciers, mineral deposits, and oceans.

If the gravity measurement for a place is changing, this could mean that the place is losing mass because of a retreating glacier or gaining mass if, as in the ocean surrounding Antarctica, new melt water is streaming in.

The Gravity Recovery and Climate Experiment, or GRACE for short, consists of a pair of satellites moving in an orbit that takes them over the South and North Poles. The two craft, nicknamed Tom and Jerry after the television cartoon characters, send constant signals to each other to determine their relative spacing to about 10 microns -- one-tenth the width of a human hair -- over a distance of 130 miles. If the first craft flies above a slightly more weighty area of the Earths' surface -- like a mountain range -- it will be tugged a bit out of place, an effect picked up by a change in the relative spacing of the craft.

http://www.physorg.com/news/2010-11-satellites-reveal-differences-sea.html