Saturday, October 11, 2014

Freeze-Up Progress

After a much colder start to October (first 10 days) than in the past five years, freeze-up is getting under way on area rivers a little early this year.  Through October 10, Fairbanks airport has seen 37 freezing degree days, compared to a 1981-2010 median of 9.5 by this date.  The total of over 3 times the normal for the date sounds like a significant anomaly, but owing to the typically rapid drop-off in temperatures at this time of year, it is only 4 days ahead of normal.

Here are a few webcam images of freeze-up progress at various locations, starting with today and going back about a week:

Tanana River at Nenana today:

Koyuk River from Koyuk today:

Koyuk River on Thursday Oct 9:

First widespread ice on Teshekpuk Lake, close to the Arctic coast, on Tuesday Oct 7:

 Teshekpuk Lake the next day, Wednesday Oct 8:

First ice cover on the lake at Inigok, between Umiat and Tesh Lake, last Saturday Oct 4:

And finally, a grainy shot of Toolik Lake (near the haul road just north of the Brooks Range) freezing over last Friday Oct 3:

Here's a chart showing the lake and air temperatures during the freeze-up of Toolik Lake.  I'm not sure of the depth of the temperature sensor in the lake, but it shows nicely how the temperature stabilized at about 2 °C in tandem with the freeze-up.  No ice was evident on the lake until this temperature threshold was reached, but since freezing began there has been only a tiny amount of additional cooling.  This nicely illustrates the heat exchange processes that are so important in the freezing of fresh water lakes around the world.

1 comment:

  1. The rule we used to use to predict imminent freezing of lakes was ~39F/4C, the temp of max density of water. As temps drop the lake surface will cool to near 4C then mixing of the lake top to bottom can occur. Lake depth and wind influence the rate and timing of this annual event. Once it mixes the surface temp is cool enough to drop even further, expand, and form ice crystals.

    I carry a water thermometer when flying on floats. It's time to get out of the water when it hits 4C or cooler. Nothing like chipping ice out around a plane and taxiing through frozen pans and slush to make you pay more attention next time.