NASA - Aqua Mission logo.
Feb. 26, 2014
On February 19, 2014 the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite flew over the Great Lakes and captured this striking false-colored image of the heavily frozen Great Lakes – one of the hardest freeze-ups in four decades.
According to the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory (GLERL), ice cover on North America’s Great Lakes peaked at 88.42% on February 12-13 – a percentage not recorded since 1994. The ice extent has surpassed 80% just five times in four decades. The average maximum ice extent since 1973 is just over 50%.
Unusually cold temperatures in the first two months of the year, especially in January, are responsible for the high ice coverage. Very cold air blowing over the surface of the water removes heat from the water at the surface. When the surface temperature drops to freezing, a thin layer of surface ice begins to form. Once ice formation begins, persistently cold temperatures, with or without wind, is the major factor in thickening ice.
The extreme freezing of the lakes is an unusual sight for residents, and has brought tourists flocking to certain locations, such as the Apostle Islands National Lakeshore, where Lake Superior’s thick ice has thousands trekking about 1 mile across the lake to visit spectacular frozen ice caves. Frozen lakes also means an end to lake-effect snow – snow that forms when cold, dry air passes over a lake, gaining moisture, then is dumped on the far side. However, ice interferes with marine commerce, pleasure boating and fishing, all of which depend on navigable waterways. It also closes the lakes to migratory birds which flock here in the winter time. Some species, such as White-winged Scoter and Red-necked Grebe, have shifted away, and are being seen in great numbers as far away as Maryland.
In this false-color image, which uses a combination of shortwave infrared, near infrared and red (MODIS bands 7,2,1) to help distinguish ice from snow, water and clouds. Open, unfrozen water appears inky blue-black. Ice is pale blue, with thicker ice appearing brighter and thin, melting ice appearing a darker true-blue. Snow appears blue-green. Clouds are white to blue-green, with the colder or icy clouds appearing blue-green to blue.
NASA’s Aqua satellite
On the day this image was captured, according to NOAA GLERL, the ice concentration covering the great lakes were as follows: Superior, 91.76%; Michigan, 60.35%, Huron 94.63%, Erie, 92.79%, Ontario 20.78% and Lake Saint Claire, 98.78%, making for a total ice concentration of 80.29%. This is less than peak, suggesting that the warmer temperatures in mid-February have allowed some thawing. Temperatures are once again expected to plummet, however, thanks to another “polar vortex” bringing arctic air to the region. NOAA predicts that Friday, February 28 will be the peak of the next arctic outbreak, with lows dropping below 0°F across Michigan.
For more information about NASA’s Aqua satellite mission, visit: http://www.nasa.gov/mission_pages/aqua/
Images, Text, Credit: NASA/Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC.
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