Take a few steps outside, and there's no escaping it - it's winter. The air is crisp and cold, frost laces the grass, and dark closes in earlier each day.
But why? What causes animals to develop thick coats, or water to run in a ditch when, all around, puddles are frozen? For a city dweller, winter can be a nuisance, causing snow days and sliding cars. But when crops or livestock are on the line, knowing the whys and hows of winter is more important - for even small farms, that can mean the difference between profit and loss, success and foreclosure.
Why winter in the first place?
Chalk that up to the tilt of the earth. The planet rotates on its axis once every 24 hours - that's what makes night and day - but it also tilts to one side. If the Northern Hemisphere is closer to the sun, it will be summer there and winter in the Southern Hemisphere, and vice versa. If the earth's axis were perpendicular to its orbit, there wouldn't be seasons.
"We could pick the climate we wanted based on how far away from the equator we were," said Todd Bronson, assistant professor of chemistry at the College of Southern Idaho. And if the earth didn't rotate, and the U.S. happened to be on the side turned away from the sun, we wouldn't have days. "If we didn't get any sun, we'd be frozen solid right now."
Because the earth does rotate, and it does tilt relative to the sun, the planet has seasons, and daylight hours get shorter for half the year. With less sun shining down, it gets colder.
Of course, other factors play a role as well, including global changes in climate like the one most scientists agree the planet is undergoing. Longtime southern Idaho residents like retired farmer Francis Karel of Buhl have noticed a change in just a few decades.
"I don't think we're getting as much snow now as we used to, 20 or 25 years ago or earlier," Karel said. When he was growing up in the '40s and '50s, he said, his family had to shovel out after a big snow as many as a dozen times a year, while last year he had to break out the tractors only twice.
Thicker coats and shedding trees
It may be easier to get around now, but Karel wishes winters would get harder again, because less snowfall means less water in the spring, which spells danger to crops.
"We're hoping we get more snow this year, and it'll turn around, because we need the water. If we don't get snow in the mountains, especially, we're in trouble," he said.
At Karel's farm, he has adjusted to accommodate cold weather. The pipes that bring water to his livestock troughs are buried three feet deep so they don't freeze, and he goes out each morning the mercury drops to break the ice at the top of the troughs. With no green pastures for grazing, he must put out alfalfa or hay to help the cows produce enough energy to fight the cold, and the diesel engines in his farm equipment require plug-in heaters to get them going on the coldest mornings.
Winter may not be Karel's favorite season. "A little bit of it goes a long ways," he said. "It's harder to get around and harder to work because you have to have more clothes on." But he has fond memories of the snowy cold, too, including the winter of 1948-49, when four feet of snow spurred him and his friends to build bobsleds out of fence posts and wooden boxes.
Dragging that bobsled was a horse, which undoubtedly had a thick winter coat. To survive, animals adapt to the same factors that cause the cold - shorter days and thus less warming sun.
"(The length of the day) has a big impact on the pineal gland. This gland secretes a hormone called melatonin that's secreted at night, not during the day," said Barry Pate, animal science instructor at CSI. This same hormone causes seasonal affective disorder in some humans, but in animals it regulates when thick, insulating winter hair begins to grow, when certain species become fertile, and when other species hibernate.
In southern Idaho, not many species truly hibernate. Some, like bears, may slow metabolism and sleep much more, but their body temperature does not approach freezing and they can be woken. In true hibernation, like that in bats or ground squirrels, the animal can't be woken until spring, and its metabolism all but stops.
"The other thing that affects coat length is cold temperatures," Pate said. Scientists believe that breathing in cold air past the thyroid gland is another trigger that winter is on the way, he said.
Plants make similar adjustments.
"As soon as the days start to shorten, a lot of plants convert their sugar into carbohydrates for winter survival," said George Mannoe, general manager at Hailey Wholesale Nursery in Gooding. "They start to lose their leaves so when they're dormant they will no longer be respirating or losing water."
Some plants grow well in cold weather, while others do not; this is attributable to differences in the composition of fluids and cell walls. "Some plants have more antifreeze in them than others," Mannoe said.
The biggest danger winter poses to trees and other plants is if they get cues that it's spring, and then are frozen again.
"For deciduous trees, it's a good idea to wrap the trunk with something that reflects light, especially in the later part of the winter when the sap starts to flow. At night (sap) will freeze and it can crack the bark," he said. The same is true for all live trees at Christmastime. "A Christmas light on a tree can give enough heat that it will break dormancy and the new growth will be killed by frost."
Most of Karel's trees have survived well over winter, except for a few. "If it gets down to 30 below or something for any length of time, it'll kill our peach trees and we have to start over," he said.
When water meets winter
The idea behind freezing sap in trees and freezing water on a lake is the same. At a certain temperature, every liquid becomes a solid. For water, that temperature is about 32 degrees, when it turns to ice.
When that water is vapor in the air, it turns to frost, falling onto lawns and windshields and leaving a fine white dusting of ice. When that water is high in the atmosphere, it falls as snow.
Depending on the temperature of the air and the ground, snow can be large, sticky flakes; tiny, smooth pellets; or a variety of other appearances. What's best for snowmen and snowball fights?
"If (flakes) form more densely or higher up, or at temperatures when they're partially liquid, they might be stickier at that point. If it's really cold, they're not going to stick together at all," Bronson said. So plan your snowball fights when the temperature is near 32 degrees for the stickiest snow.
Skiing, on the other hand, is better well below the freezing point when the snow isn't as sticky.
"When you ski, you're not sliding on snow," Bronson said. "The pressure from the blades causes the snow to melt between the skis and the snow, so you're really sliding on water."
If your pipes aren't buried as deep as Karel's, beware of using copper instead of plastic.
Water expands when it freezes, and plastic does a little but copper doesn't, so copper pipes may burst.
To prevent that, two solutions are to keep the water running a little or to empty the pipes. Motion gives the water molecules enough energy to keep them from freezing even when the temperature is below 32. This is why you may see water moving in a ditch when the puddle next to it is frozen solid.
Frozen and cold, the winter landscape is a wonder of beauty and science. Enjoy it while it lasts, as spring isn't far behind.
Ariel Hansen may be reached at 735-3376 or firstname.lastname@example.org.
|Title: Science of winter
Date: December 3rd, 2007
How well do you know your freezing facts? Take this test of winter science to find out.