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How Rectal Thermometers and Antarctic Excursions Gave Us "Wind Chill"

Creative Commons
The weather station atop Mount Washington (New Hampshire) chained down and covered in rime frost.
The wind chill chart developed in the Antarctic was meant for soldiers fighting in the cold theaters of World War II.

Temperatures have plummeted in Connecticut, with the wind chill nearly 20 degrees below zero. But how is wind chill actually calculated? To answer that question, I learned about the number's colorful -- and changing -- history.

It was the 1940s. Two scientists were in the Antarctic; it was windy -- and they decided to try an experiment.

"They had a plastic container of water and they recorded the time it took for the water to freeze, with the idea that the faster it froze, the greater would be the effect of the wind," said Maurice Bluestein, a professor of mechanical engineering, and one of the scientists responsible for the latest iteration of the wind chill chart.

It got redrafted in 2001, and today, it's what meteorologists across North America use when they tell you, "It's ten below outside -- but it feels like 21 degrees below zero." 

"It represents the effect that the wind has on the rate at which you lose heat from the body," said Bluestein. He said the wind chill chart developed in the Antarctic was meant for soldiers fighting in the cold theaters of World War II. It stood for decades, but as heat transfer theory developed, scientists realized there was a need to update and refine the equations.

Credit RicHard-59 / Wikimedia Commons
Wikimedia Commons
The Windchill effect.

Eli Jacks is a meteorologist at the National Weather Service. He said Bluestein's equations focused on heat loss through the face -- the part of the body most likely to be exposed during cold weather. And there were other assumptions, too. "It also corrected for a height of 5 feet," he said. "It incorporated some more modern heat transfer theory. It assumes a certain walking speed, because of course that factors into the speed as you experience the air on your face."

After developing his equations -- Bluestein said volunteers were recruited to make sure the numbers made sense. A dozen men and women were outfitted with rectal thermometers, cheek sensors, and hooked up to treadmills while cold air was blown in their face.

"These were volunteers from the military, the Canadian military. Who else would want to volunteer for something like that?" Bluestein said.

But the equations proved surprisingly accurate. Tolearn more about the history of wind chill, check out WNPR's Science Blog,The Beaker

Patrick Skahill is a reporter and digital editor at Connecticut Public. Prior to becoming a reporter, he was the founding producer of Connecticut Public Radio's The Colin McEnroe Show, which began in 2009. Patrick's reporting has appeared on NPR's Morning Edition, Here & Now, and All Things Considered. He has also reported for the Marketplace Morning Report. He can be reached at pskahill@ctpublic.org.

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