There has been considerable interest in the recent state of Arctic sea ice for scientific research and for operational applications especially along the Northern Sea Route and the Northwest Passage. This pair of sea ice maps was derived from radar data from NASA's QuikScat satellite scatterometer on September 2, 2008 (left panel) and September 5, 2008 (right panel).

QuikScat's unique features make it a powerful tool for mapping sea ice and accurately identifying sea ice conditions. It can distinguish sea ice from open water, differentiate different classes of ice, and compensate for effects of strong winds on ocean surfaces and effects of melt on ice.

In the above images, red areas denote sea ice that was undergoing active melting on the ice surface, magenta areas show sea ice with reduced melt, cyan areas are refrozen sea ice that had some residual wetness from earlier melting, and white areas represent sea ice that had been refrozen for 10 or more days.

Ocean areas with less than 15 percent ice cover on the surface are blue, while land surfaces are shown in brown and missing data are depicted in black.

Along the coast of Siberia, the Northern Sea Route was blocked by ice in an area northeast of Taymyr Peninsula (denoted by the black "T") on September 2.

Just three days later, on September 5, an ocean path was observed in the same area. Warm air transported by northward winds led to extensive areas of active melt (red) over a larger region extending from the Barents Sea across the Kara Sea to the Laptev Sea on September 5.

That melt event was so large that some parts of it reached as far north as the vicinity of the North Pole.

Along the Canadian north coast, the Northwest Passage was blocked in the Parry Channel north of Victoria Island (denoted by the black "V") on both of these dates, and ice in the small straits south of Victoria Island was slightly reduced on September 5 compared to that on September 2. Very little active melt (red) was observed in the Canadian Arctic Archipelago on both dates.

The sea routes may be opened or closed rapidly by transient weather events. Such unstable sea ice conditions in the passages can cause a significant navigation risk.

The total sea ice extent in the Arctic at this time was about 0.5 million square kilometers (0.2 mission square miles) larger than that at the same time last year. That difference in sea ice extent amounts to an area the size of Spain.

QuikSCAT, managed by JPL, measures ocean surface wind/stress by sending radar pulses to the surface and measuring the strength of the signals returned.