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Greenland Sea Ice
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Greenland Sea Ice

August 7, 2012
In late July, 2012, sea ice and clouds formed an intricate pattern over the Greenland Sea as the summer melt progresses. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite captured this true-color image on July 28, 2012.

A part of Greenland’s surface ice sheet melts each summer, with most of the high-elevation ice quickly refreezing in place. Near the coast, some of the annual melt remains as part of the ice sheet, and some is lost to the ocean. The amount of melting varies somewhat each year.

In summer of 2012, the melting of Greenland’s ice sheet has been unusually widespread. According to measurements from four satellites (MODIS on Aqua and Terra, the U.S. Air Force’s DMSP satellite, and India’s OceanSat-2, and an analysis by NASA and university scientists, an estimated 97 percent of the top layer of the ice sheet had thawed at some point in mid-July, the largest extent of surface melting observed in three decades of satellite observations.

The near-total surface melt was so unusual, that the scientists analyzing the data at first thought the anomaly was due to a data error rather than true ice conditions. Comparing the radar data from OceanSat-2 with MODIS imagery confirmed unusually high temperatures over the ice sheet surface and that the melt was extensive. Passive-microwave data from the DMSP also confirmed the melt.

The extreme melting coincided with an unusually strong ridge of warm air over Greenland, which brought air temperatures at the Summit Station, near the highest point of the ice sheet, above or within a degree of freezing for several hours from July 11 to July 12. Melting events in Greenland have occurred before – the last one was about 1889 – causing scientists to estimate that there may be a cycle of about 150 years for such events.

Credits: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC