Posted at 4:47 PM on February 23, 2009
by Paul Huttner
A cloudy Highway 1 near Ely today. On sunny days, pine trees in coniferous forests can create warmer microclimates "up north."
It's good to get away to northern Minnesota for us city folk.
My weekend in the Brainerd Lakes area was full of fun and relaxation as usual. A cool foot of snow still covers the ground, much to the delight of snowmobilers. The northern landscape still lies in winter's grip, but signs of seasonal change can be seen with a sharp eye.
The higher late February sun melts away road surfaces much faster now. And if you stand on the sunny side of a pine tree, even when it's 15 degrees it feels pretty nice if there's no wind. That's because you're standing in a microclimate. The sun's rays bounce off the tree, converting the radiation from short wave to longer wavelengths. These longer wavelengths are more effective at heating the surrounding air and you feel warmer.
Now multiply that effect by what, 100 million pine and spruce trees in northern Minnesota? You can see why on sunny, calm days in northern Minnesota in late winter thermometers respond with warmer temps than in the metro or the farm fields of the south. Even in the same air mass it's often warmer up north.
You can thank "Big Al" or albedo for the difference. A snow covered landscape will reflect about 80 to 90 percent of the sun's energy back into space. A coniferous forest only reflects back about 10 to 15 percent. The rest of the energy is available to heat the surrounding air.
We live in an amazing state. There is always plenty of weather and scenery to enjoy!
Thanks for the great reminder about "Big Al." I remember a great chart from freshman physical geography showing the energy flow on a sunny winter day, from sun to conifer needles to snow to person...I even asked the professor for a copy of his overhead. I spend most of my time in these northern forests and forget about the wide open white land in the southern part of the state. Hanging out in Ely, it feels like all the factors are stacked in favor of cold, but those dark conifers really do capture the sun's warmth.
You should have more posts like this, talking about causes behind weather patterns and larger, year-scale trends, rather than current weather events which we can read about anywhere.
I've lived in Minnesota all my life and only learned about the January Thaw as a phenomenon this year, so a lot of these things really could stand to be discussed more.