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Sea ice is frozen seawater floating on the surface of the ocean, typically averaging a few meters in thickness. Some sea ice is semi-permanent, persisting from year to year, and some is seasonal, melting and refreezing from season to season. This animation shows how the seasonal global sea ice has changed from day to day since 2002, when the Aqua satellite was launched. The AMSR-E instrument on the Aqua satellite acquires high resolution measurements of the 89 GHz brightness temperature and sea ice concentration near the poles. This sensor is able to observe the entire polar region every day, even through clouds and snowfall, because it is not very sensitive to atmospheric effects. The false color of the sea ice, derived from the AMSR-E 6.25 km 89 GHz brightness temperature, highlights the fissures or divergence areas in the sea ice cover by warm brightness temperatures (in blue) while cold brightness temperatures, shown in brighter white, represent consolidated sea ice. The sea ice edge identifies areas containing at least 15% ice concentration in the three-day moving average of the AMSR-E 12.5 km sea ice concentration data. This sequence shows the daily global sea ice over both the Arctic and Antarctic on a Cartesian grid from June 21, 2002 through December 31, 2008 at a frame rate of four frames per day. On days when data is not available, the prior or following day's data is used. Periods when data was absent for several consecutive days include: 2002/07/29 through 2002/08/08, 2002/09/11 through 2002/09/20, and 2003/10/29 through 2003/11/03.
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