In a rapid response to the cooler - though still much warmer than normal - conditions, ice has begun to form on inland waterways across northern Alaska. The webcam photo below, courtesy of Pro Music in downtown Fairbanks, shows some thin ice on the Chena River, and FAA webcams reveal a similar situation on the Yukon River at Beaver and the Koyuk River at Koyuk (also shown below). It is interesting that in the case of Koyuk, the lowest the temperature has dropped is 27 °F, but with a stiff breeze today, that is all it took to begin the process of freeze-up.
Also of interest is the view from Kivalina, on the Chukchi Sea coast northwest of Kotzebue. Despite temperatures only dropping below freezing yesterday evening, and a morning low temperature of only 24 °F, the lagoon behind Kivalina shows a substantial amount of ice today. There's just no getting around the inevitable for this time of year.
Once the water hits ~ 4C it soon ends the wet season providing even cooler temps follow. Density of water colder than that decreases, and unless well mixed by wind or current, stratification and reduced mixing by temperature occurs either vertically in the water column, or in shallows along the shore. The upper layers of water exposed to cold air soon loose heat especially on clear calm days and nights.
ReplyDeleteThe Fairbanks Airport float pond skimmed over in most parts with thin ice yesterday about 10 days late. Deep lakes and gravel pits in Alaska's interior with a large volume of water will take weeks more to finally form an ice cover. Unless it soon blows to remix or substantially warm the water another sign of winter will have arrived.
Gary
Thanks for the insight, Gary. I am used to seeing freeze-up in more southern latitudes where many days of significantly below-freezing temperatures are needed to generate ice. I wonder if the primary difference is that in permafrost-land, (non-surface) ground water is never much above freezing and therefore river water hits 32 very quickly when air temperatures drop below the threshold. What are typical summer water temperatures in interior Alaska rivers?
DeleteHello Richard. Yes I suspect you're correct about the relatively cold ground water influencing the rate of freezing of lotic and lentic waterbodies in Alaska. Local deep wells in the Fairbanks area run 2-4C depending upon the aquifer.
DeleteHere's some summer obs regarding water temps:
http://www.adfg.alaska.gov/FedAidpdfs/RIR.3A.2011.05.pdf
http://ak.water.usgs.gov/Publications/pdf.reps/wrir99.4204.pdf
http://or.water.usgs.gov/pubs_dir/WRIR01-4109/wrir014109_4.pdf
Gary
Thanks Gary. Lotic versus lentic... I learned something today. Thanks for the links - very interesting, particular the Yukon basin overview. Wish I had time to read the whole thing properly.
DeleteAnother thing to consider is the length of day (or lack thereof). A day with a low of 28 and a high of 40 in Fairbanks in late October is quite different than a day with a similar temperature range at 35° N latitude (for example). In Fairbanks, perhaps 18 or 19 hours of the day are spent below freezing and only a few are spent above freezing. Plus, the maximum solar angle is about 12 degrees above the horizon and most of the sun's rays are shaded out by trees or topography. And lastly, the albedo of water is quite high with the low sun angle so direct solar heating is quite minimal for those areas where the sun's rays make it to the water surface. Conversely, in mid latitudes, on a day with a low of 28 and a high of 40, only a few hours are likely spent below freezing and a lot of the sun's energy is absorbed directly by the water.
DeleteNice collection of images Richard. Thanks. Useful discussion too.
DeleteBrian,
DeleteThose are really excellent points that go a long way to helping explain the observed behavior. The situation was nicely illustrated in Fairbanks yesterday: a high of 43, low of 21, for a daily mean of 32, but only 6 hourly observations were above freezing. This highlights a deficiency in the simplistic method of calculating daily mean temperature as the average of the high and the low; we really should be using hourly temperatures.
This is news. I assumed that avg daily temps included a mean of available hourly observations. Do "they" really only take the high and low and divide by 2?
DeleteGary
It's worse than that Gary. They don't even use a decimal point if the two days add up to an odd number!
DeleteGary, correct... it's usually a simple average of the high and low, rounding up the result as Brian said. I am not sure of the origins of this procedure, but suspect it may have to do with degree-day calculations. Standard practice is to compute degree days as integers, and with historical data only widely available in daily form, the simple average makes sense as a first cut.
DeleteIt's another example of something that tends to work satisfactorily in lower latitudes but not in Alaska. It seems the presence of a daytime inversion might be a key factor that prevents temperature from approximating a sine wave through a typical 24 hour period. One could probably write an interesting little paper on this.
I believe the very best part of freezing water are the sounds that are made during the process.
ReplyDeleteWhen camped next to a lake in a warm tent on a quiet day the air will be filled with booming sounds when ice forms, expands, and cracks. Especially on a clear cold night.
Rivers make a whirring crashing noise as ice flows spin and bump into each other and the river's bank. Great stuff to experience.
Gary
Found this re: Lake ice forming.
Deletehttp://www.allwaysnorth.com/Tenaya1-13am2UW.wav
Gary
Thanks, that's fascinating!
DeleteI'll add this common image for the record then be done. The cracks are the remaining physical evidence of the sounds above.
Deletehttp://www.e-mongol.com/images/Mongolia%20-%20Mongolie%20-%20ice%20of%20khovsgol%20lake.jpg
Gary