MODIS
March 12, 2003
http://earthobservatory.nasa.gov
Large lakes, like Lake Superior, rarely freeze over. This is largely due to the effects of winds, which destroy the continuity of ice cover. The photo above shows an ice cover of about 90%, which has occurred only once or twice in the last decade. Ice cover changes the solar heating pattern by reflecting instead of absorbing solar energy.
Although Lake Superior experiences temperatures low enough to freeze its surface, it also is affected by stronger winds. Winds break up the ice and move it.
Ice breakup can occur quickly. This sequence of images is from MODIS satellite imagery. The images are from March 4-8, 2010 at 18Z (1PM EST) daily, for Lake Erie.
Average date ice cover >or= 10%: A sample of the digitized total ice concentration for the Great Lakes. This is the data for February 13, 1975. Project: Lambert, Spheroid Clarke 1866. Total ice area for all Lakes: 130,712 square km. Percent Ice Cover for all lakes: 51.42%.
NOAA GLERL
How lake ice plays a huge role in Lake dynamics:
Evaporation of the lake occurs mainly in fall and winter, not in the summer. When there is no ice cover of the lake in winter, evaporation is even greater. Much of the winter evaporation falls as precipitation outside of the Lake basin, so lake levels are very likely to decrease after ice free winters. Icy covers of the lake have the opposite effect. (read National Geographic report).
