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Cold Snap brings Sharp Thermal Gradients through Ice

8 February 2021

Recent cold weather throughout Alaska is good for growing ice! If thermal gradients (the temperature difference between air and water) are steep, that means more heat from relatively warm water (just above freezing) is being lost to very cold air (-40 deg C or F in recent days) to form ice. Looking at our snow-ice buoys located on lakes and ponds around the state provide a good look at these thermal gradients. For example, two of the coldest places in today were Venetie where the ice is about 105 cm thick on Big Lake and air temps of -42 C are making thermal gradients of 40 C / meter and Nuiqsut where ice is about 145 cm thick on a small pond and air temps of -36 C are making thermal gradients of 24 C / meter. So which lake is making more ice right now?

Lakes in other parts of the state have weaker thermal gradients because lots of snow blanketing and insulating the ice. West Two, Shageluk, and Tsa' Bene' lakes for example.

We also need to be cautions when interpreting buoy data as other factors like snow ice formation and overflow can cause our sensor to be at different depth than we originally intended. For example, on our recent January Shakedown Trip we recently visited Sam Charley Oxbow near Fairbanks and found 67 cm of ice even though the sensors where telling us 40 cm. About 20 cm of snow ice had formed above the buoy surface causing this discrepancy. For buoys located near Community-based Monitoring Teams, we developed a Fresh Eyes Lesson Plan to explore data from snow-ice buoys and help Fresh Eyes scientists make corrections to these data.

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