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 07.24.17

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AL*ASK*A SCIENTIST

We regret that we are no longer accepting new questions for our Alaska Scientist section. Please enjoy the past questions and answers, and thank you to those who have contributed questions or assisted with answers.

Q: Why doesn’t Alaska’s temperature rise over 100 degrees?
Lisa Ahmadian, Missouri

The temperature in Alaska actually has reached 100 degrees, during a record heat in Fort Yukon on June 27, 1915. Fort Yukon (just below the arctic circle at 66°34’ N) is located in Alaska’s Interior. Here, in the massive landlocked portion of the state, temperatures are both colder and hotter than anywhere else in the state – even than they are much farther south, on Alaska’s coastal peninsula.

While it’s pretty rare for the temperature to reach 100, who’s to say it might not soar higher on another hot summer day? After all, records were meant to be broken!

High temperatures occur because Alaska gets a lot of solar radiation. The summer days are long, particularly in the far north, and the days are often clear in the Interior, which essentiallyl has a desert climate. Lots of sunlight translates into hot weather. Highs in the 80s occur an average of 10 to 15 days per summer and are common by early July. Temperatures in the 90s, however, are rare.

This is largely due to the tilt of the earth, which causes the sun to hang low on the horizon. At the Arctic Circle, high noon on the longest day of the year sees the sun hovering lazily at a mere 47 degrees off the horizon. By contrast, in the southern United States the sun can be almost directly overhead, at an 80 degree angle.

Ever heard of the phrase “the long rays of the sun” to describe morning or evening light? At this time of day, everywhere on the globe, the sun sits at a low angle. The poetic use of the word “long” is scientifically accurate: these rays have a longer distance to travel than those from overhead. When solar radiation passes through atmosphere, particles in the atmosphere deflect or absorb some of its energy. So – the longer the trip, the more energy lost.

To see this effect, try a simple experiment. Shine a flashlight on a sheet of paper from directly overhead and mark the outline of the illuminated circle. Next, hold the flashlight at a 45° angle. The illuminated circle will be larger, but weaker, as light on the edges has dissipated.

In the same sense, a hot summer day in the sub arctic can really only get to be just so hot!

Martha Shulski, climatologist
University of Alaska Fairbanks Geophysical Institute


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