Snowy science lessons
From the afternoon of Friday, Feb. 5 through the afternoon of Tuesday Feb. 9, I spent roughly eight hours shoveling snow, thanks to the record-breaking “Snowmageddon” that brought two to three feet–in some cases even more–of snow to the Washington, D.C. area.
Shoveling snow is a good time to think about the science of winter storms, ice, and even some basic physics.
Some of the ideas and questions below, which came to me as I shoveled, could help science teachers and broadcast meteorologists help students and viewers learn more about not only meteorology but even a little basic science.
Where did it all come from?
On Friday a satellite image of the North and Central America showed a band of clouds stretching from the tropical Pacific south and west of Mexico and Central America into the storm over the eastern United States.
The clouds indicated that an “atmospheric river” was feeding humid tropical air into the storm. I describe atmospheric rivers on pages 113 and 114 and 225-226 of The AMS Weather Book. Briefly, an atmospheric river is a low-level jet stream that brings very humid air into the middle latitudes.
The Capital Weather Gang’s report on “The incredible output of Snowmageddon” includes a loop of satellite water vapor images from Feb. 4 that shows the humidity feeding into the storm the day before it hit the Washington area. (This image is the second one down from the top.)
Satellite water vapor images show the infrared signal of water vapor concentrations in the atmosphere that we otherwise can’t see. The whiter the image, the more water vapor. Chapter 7 of The AMS Weather Book covers the basics of weather satellites, including the importance of infrared images.
You can learn more from the University of Wisconsin Space Science and Engineering Center’s online “Fundamentals of Water Vapor Channel Satellite Imagery.”
The Weather Gang’s article, by the way, explains all of the factors that went into making the storm a record breaker.
If you are serious about collecting weather data, and would like to make accurate reports to the National Weather Service it’s not as simple as sticking a yard stick in the snow.
To see how the NWS measures snowfall, download its PDF file giving “Snow measurement guidelines.”
Can thermodynamics explain icicles?
Saturday morning when I saw the curved icicles hanging from our roof I recalled that the latent heat released when an icicles ice form helps explain their shape.
I’m sure the icicles are curved because a relatively light wind was blowing toward the house as they formed.
The best explanation I’ve found on how icicles form is the text and video from the Feb. 1, 2007 Science Daily on “Why Icicles are Long and Thin.
I like this because it uses physics and math to explain something anyone who lives anyplace where below freezing temperatures occur is familiar with.
If you wonder about this kind of thing maybe you’re cut out to be a scientist.
The text and video explain how the release of latent heat gives icicles their shape. For a good background on latent heat, including the story of the scientists who first figured it out, go to Page 80 of the AMS Weather Book.
When I saw the hunk of ice above the icicles–it stretches the length of the roof–I thought of the ice cornices that in publications that I had consulted when doing stories and graphics about about avalanches, like in the diagram of a cornice on a mountain on the United States Search and Rescue Task Force Web site Avalanche page. (Scroll down a couple of pages.)
On a roof, a cornice like this shows that ice damming is probably occurring, with water trapped under the ice, which could be forcing up shingles and otherwise finding its way inside. Fortunately, we have a metal roof that an attic inspection showed it is doing fine. But the ice cornice also shows that we need to insulate the attic better to keep so much heat from reaching the roof.
Where’s global warming when you need it?
No real climate scientist has ever said that a warmer world will cancel the seasons. Even though human actions are affecting the climate, including increasing earth’s average temperature, day-to-day weather continues with cold outbreaks, storms in some places and droughts in others. As I shoveled snow I realized that the U.S. Middle Atlantic and Northeast are only a small part of the globe.
In fact, the Arctic continues to have an unusually warm winter, as shown in the image to the left. It shows global temperatures compared with average on Feb. 9.
This image is an updated version of the one published with my report on “Science stories about Arctic blasts missing in action” in January.
The image to the left shows part of the complete global image for the date. It’s one in an series showing daily temperature anomalies for each day for the most recent seven days.
On the topic of global warming and winter weather, Paul Gross of WDIV-TV in Detroit says, “One of the most important points I make about global warming is that the warming does NOT replace natural variability. We’ll still have winter, and we’ll still have snow storms. However, on average, we’ll have fewer extreme cold spells, and more extreme heat waves, but that doesn’t necessarily mean fewer winter storms.”
For an extended discussion of the February storms and climate change you can read Dr. Jeff Master’s Feb. 8 Wunderblog.
More on using weather to teach science