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|Ice coverage on Lake Superior on January 9 from 2006 - 2014. White is ice, blue is water. Dan Titze, Large Lakes Observatory|
The Great Lakes are seeing more ice coverage earlier than normal this year, due to a very chilly December and the recent southward excursion of the polar vortex.
The polar vortex is a persistent feature of the Earth’s atmosphere, in which extremely cold air located in the upper atmosphere circulates around the north and south poles. Occasionally, the northern polar vortex can develop an instability, migrating south or even spinning off separate blobs of arctic air into Asia, Europe, and North America.
This year it dipped into Canada and pushed cold weather into the Midwest and further. It was severe. The National Weather Service reported on January 7 that about 1.5 million square miles — or half of the lower 48 states — had wind chills below zero. The polar vortex, combined with the exceptionally low temperatures in December and early January, also had an impact on Lake Superior.
LOTS MORE ICE
Jay Austin, associate professor at the University of Minnesota Duluth’s Large Lakes Observatory and Department of Physics, said, "The ice coverage is up, way up. So far this winter, they are far higher than what we have observed at this time of year in over a decade.”
While ice cover can reduce the amount of lake-effect snow downwind of the lakes, the jury is out on the impact it has on lake level. “Work done by some of my colleagues suggests that while ice cover suppresses evaporation, it usually follows a particularly cold fall and early winter," Austin said. “These cold seasons typically result in higher evaporation rates. The data suggest that ice cover may not play as large of a role in lake level changes as previously thought.” One other consequence of high ice levels is that they typically lead to cooler lake temperatures the following summer.
Dan Titze, a graduate student who works with Austin at the Large Lakes Observatory, prepared the images on this page.
Story by Cheryl Reitan. January, 2014.
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