Disappearing Sun; Barrow Update

Today marks the day when the sun's angle above the horizon at solar noon has declined half way from the equinox to the winter solstice; or equivalently we have traveled three-quarters of the way from the summer to winter solstice in terms of the sun's elevation at noon.

What does this mean?  It means we hereby enter the dark third of the year in the northern hemisphere; and of course this fact is more inescapable the farther north you go.  We can illustrate the lack of solar energy across Alaska in winter by calculating the theoretical solar insolation under clear skies.  From this theoretical standpoint, the total solar energy received in Fairbanks over the next 4 months is less than is received in 6 days in the height of summer.  In Bettles the dark third of the year receives less radiation than in 4 days in summer.  However, in Anchorage the winter sun provides the equivalent of about 10 days in summer.

Here's the view at close to solar noon yesterday from the Alaska Climate Research Center webcam on UAF West Ridge.  The weakness of the sun is illustrated by the fact that some snow remains on the ground despite most days getting above freezing in the past two weeks; the official snow depth in Fairbanks has been at 1 inch for 10 days now.

On another note, Barrow has had a chilly and very windy time of it in the past several days, with a very strong pressure gradient importing cold Arctic air from the northeast.  Here's the surface analysis from Monday afternoon when winds were sustained at about 40 mph for a time.

The high temperature on Tuesday was only 17 °F in Barrow, which is the coldest day so early in the season since 2002.  As we've mentioned many times before, Octobers since 2002 have been extremely warm in Barrow compared to previous decades, and so this kind of chill would have been completely normal in the last century.  For example, the 1930-2000 normal for coldest high temperature to have occurred by October 21 in Barrow was 10 °F; and a high temperature of 17 °F would normally have been observed by October 12.  In 1996, when sea ice was firmly established from Barrow eastward by late September, the high temperature was -7 °F on October 11!

So, it's been a little cooler in Barrow in the past few days - but even this is only approaching normal from earlier decades.  October 2014 is still running well above both the 1981-2010 and 1971-2000 normals.