Looking at the temperatures in Barrow since the beginning of October, it is evident that warm temperatures have been the rule. In fact, 77% of the days between October 1st and February 12th have been above normal.
The first chart shows the average daily temperature departure from normal (1981-2010) during that time period. Since October 1st, the average day has been 7.5°F above normal.
The second chart shows the same information as the first but instead of daily temperature departure measured in degrees Fahrenheit, it shows the daily departure in standard deviations. The median daily departure from normal as measured in standard deviations was 0.67 based on the 1981-2010 climate normal period. According to a standard z-score table, 25% of days should be more than 0.67 standard deviations above the mean – not 50%.
Finally, the last chart shows the average temperature between October 1st and February 11th for each winter since '20-'21 until the present. The current winter is far and away the warmest during those 90+ years – by 2.1°F! There is data that goes back before 1920 at Barrow but it has significant data quality issues. Still, this year is warmer than any complete year prior to 1920 as well. Certainly the lateness of the sea ice in recent decades has significantly contributed to early season warming in particular.
*Update Section*
The two maps below are from the ESRL Reanalysis data sets. The first map shows the temperature anomalies for Alaska during the months of October through December for the last 10 years. The second map shows the temperature anomalies for Alaska during the months of February through April for the last 10 years. The lack of sea ice in the Fall and early winter dramatically warms the northern portions of Alaska. Once the winter ice pack has set in, the temperature anomalies are greatly reduced. On the second map you can see the cold anomaly in the southeast Bering Sea due to high spring ice extents and cold water temperatures.
I'm sure that there has been papers done on this...two comments:
ReplyDelete1. If you strain your eyes you can see slightly lower temps from the 40's to 70's. This is similar to the general worldwide trend. Maybe PDO? But then there is the wholesale collapse of minimum temps as stated in a previous post. So how much of this warming is advection from the south and how much is from the Arctic north?
2. Similarly, we have the chicken and the egg in the snow problem. Is the rise in temps due to a lack of sea ice? Or is the sea ice low due to a lack of temps? Or, more likely, what percentage of both?
Thank you for the comment Eric. I added a couple of maps from the ESRL Reanalysis site showing 10-year temperature anomalies during Fall and also during Winter.
DeleteTo answer your questions,
1) Yes, the PDO shift in the mid 70s is apparent in the chart. The shift is more pronounced in most parts of Alaska but it is definitely there. The maps I added to the post pretty clearly demonstrate that the warming is most pronounced at higher latitudes so it would not seem likely that warm air is advecting northward.
2) Given that the specific heat value for open water is 3 to 6 times greater than it is for bare ground, you can think of open water as a bank that stores heat. Since there is little solar energy in the late Fall and the temperatures have been way above normal, it is safe to assume that the warmth radiating from the open water is the source of the temperature anomalies - regardless of the amount of snow on the ground.
News and links to source regarding freshwater lakes near Barrow:
ReplyDeletehttp://www.alaskadispatch.com/article/20140211/study-some-arctic-alaska-lakes-icing-later-thawing-earlier
Many of the deeper lakes are isolated and contain resident populations of fish...ancient Lake Trout, various whitefish, and other species. You can see the freeze depth when flying over. Bare sandy shore boundaries down to 2M+ that encircle vegetative growth in deeper waters are clearly visible. Was over all that country sampling fish flying out of Umiat back in the early 1980's.
For a look at what I've described, Google Teshepuk Lake and zoom into the smaller lakes surrounding W>S>E with satellite view.
Gary
Gary,
DeleteIt is an interesting physical phenomenon that not all the lakes are frozen solid in the winter up there. From Brian, the annual mean temp is 11.5F, yet we have liquid water atop the permafrost all year round. Curious.
Richard
Yes it's curious given the location and Barrow's prevailing temps.
DeleteHowever, even though Barrow, Deadhorse, Kaltovik and other coastal reporting stations are mainly influenced by their proximity to the adjacent marine environment, inland areas towards the southerly Brooks Range are influenced by both the marine and North Slope terrestrial land mass.
Depends on the prevailing wind in ice free periods. Winds from the north and west (coastal) often bring cool and wet. Flow from the south or southeast, or none at all, create a quite warm environment in summer.
If you look closely at the Google scan of lakes noted above, you'll see a distinct NW>SE orientation of the lakes. That's due to the winds that prevail during ice free periods melting permafrost and expanding the waterbody through wave action. The soils are sandy and easily displaced once melted.
Scan for Umiat or Galbraith Lake's seasonal temperatures and note the potential for extreme warmth during the summer's continual photoperiod and insolation. I assume there's enough residual heat in lakes deeper than 2-3M and the soils below to prevent complete freezing during the winter.
Find fish in a lake without an inlet or outlet and I'll guarantee it doesn't freeze completely. From the Google view, the deeper the blue in the middle of the lake the deeper the water.
Gary
Good information, thanks. Further reflection suggests that the situation is nearly inevitable given the low thermal conductivity of water and ice, the density-temperature relationship of fresh water, and of course the reduced density of ice compared to water. If ice were an infinitely poor conductor, then the thinnest layer of ice would allow water below to remain unfrozen regardless of how cold it is above. It's a wonderful aspect of nature that allows aquatic ecosystems to thrive even in very cold environments.
DeleteWithout straying too far from the OP's topic (I hope) another factor enabling under the ice survival of aquatic species is the Colligative Property of water.
DeleteAs ice forms the concentration of total dissolved solids in the unfrozen water increases. That in turn depresses the freezing point of the liquid solution to some degree.
Think salt on the road scenario, but in a considerably weaker sense.
Gary
The comments have been very insightful. Thanks guys!
ReplyDeleteOne more excellent link Brian that follows your initial topic. This is a good parallel I believe to the noted change in air temperatures near Barrow. It details the recent changes of the thickness of freshwater lake ice.
ReplyDeletehttp://www.the-cryosphere.net/8/167/2014/tc-8-167-2014.pdf
Gary