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View Full Version : MODIS: Sea Ice in the Greenland Sea


tlr online
22-05-04, 01:12
The presence of sea ice influences the temperature and circulation patterns of both the atmosphere and the oceans. The presence of sea ice with its high albedo (the ratio of reflected light to incoming (incident) light) reduces the amount of solar radiation absorbed at the ocean surface, and along with the overlying snow cover, serves as an insulator to restrict exchanges of heat, momentum, and chemical constituents between the atmosphere and the ocean. Its large area coverage (5-8% of the ocean surface) makes sea ice cover a key parameter in the Earth’s energy balance. Ice-surface temperature controls snow metamorphosis and melt, the rate of sea ice growth and air-sea heat exchange, and is an important parameter in large-scale models.

This Terra MODIS image from March 12, 2003, showcases the Ice Surface Temperature (IST) product. The image shows the northern Greenland Sea in the Arctic Ocean, and was produced using two thermal-infrared bands (the color scale, which is visible in the 1km version, represents IST in degrees Kelvin). The approximate center point of the image is 81.7º N, 1.0º E.

Both well-developed ice floes and recently refrozen leads are evident in the image. The ice floes appear white and light blue, while the refrozen ice in the leads (the spaces between the floes) appears purple. When ice floes first break apart, unfrozen water is exposed in the leads between the floes. The ice that forms in these leads has a higher-relative temperature, and because higher relative temperatures most likely correspond with thinner ice, IST can often be used to detect new and young ice.

Note the area of the highest temperatures, shown in shades of red in the lower right part of the high-resolution 1km image. This area of “warmer ice” suggests very low ice-concentration approaching the ice edge. Open water (with an IST exceeding 271.5K) is also visible there in dark blue. Because sea ice is saline, it freezes at a temperature that is less than 273.15K, the freezing point of fresh water. A temperature cutoff of 271.5K is used for this image to illustrate the difference between water and ice. The ice edge cannot be seen on the full swath of this MODIS image due to cloudcover, but other data show the ice edge to be just beyond the areas of the highest ISTs (the red areas in this image), thus confirming that the higher ISTs are related to lower ice concentrations.

The MODIS instrument is useful for determining sea ice extent, albedo, movement, type, and concentration at resolutions ranging from 250 m to 1 km, and Ice-Surface Temperature (IST) can be determined at 1-km resolution. Daily extent and IST map products are produced at the MODIS Data Processing System (MODAPS) facility at Goddard Space Flight Center in Greenbelt, Maryland, using MODIS data at 1-km resolution. The MODIS sea ice products were developed at Goddard Space Flight Center http://modis-snow-ice.gsfc.nasa.gov, and are archived and distributed by the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado. More information about MODIS' Sea Ice Cover Product can be found here.

http://modis.gsfc.nasa.gov/gallery/images/image05212004_md.jpg

Copyright 2004 NASA

Dorothy
11-06-04, 14:11
What colours
...and the shapes remind me of organic tissues!