Engineer refined formula to calculate wind chill
On frigid winter mornings, when weather forecasters are trying to describe whether it’s a hat-scarf-gloves day or if just a warm coat will do, they will take the temperature (T) and wind speed (V) and plug the numbers into a handy equation: WCT = 35.74 + 0.6215T - 35.75(V0.16) + 0.4275T(V0.16).
The result is the wind chill index, a number that attempts to tell us how cold it might feel rather than simply how cold it is. It considers wind, in addition to temperature, to calculate the loss of heat from the body.
The National Weather Service had been calculating the wind chill since the 1970s, but not very accurately, until two scientists set out in 2001 to perfect the measure and make it more reliable. One of the two was Maurice Bluestein, who died at 76 on Aug. 28 in Pompano Beach, Fla., where he lived. His daughter Karen Bluestein said the cause was esophageal cancer. Maurice Bluestein, who was trained as a mechanical engineer, had not given much thought to the science behind the weather until he was shoveling out his daughter’s car from under a snowdrift one evening in January 1994 in Indianapolis.
It was the coldest day on record in Indiana, with temperatures reaching 25 degrees below zero Fahrenheit. The Weather Service, using the existing wind-chill formula, determined that with winds of about 15 mph, the air temperature could feel as if it were 65 degrees below zero — capable of causing frostbite within 15 seconds. Stay indoors, the service advised.
But as he shoveled away, Bluestein found that it really did not feel all that cold. “He kept taking off layers of clothing,” Karen Bluestein said in a telephone interview. “He was sweating, thinking: ‘This makes no sense. I wonder who came up with this.’” He set out to improve what he deemed an inaccurate, and alarmist, measurement for wind chill. “The old system scared people into taking unnecessary actions,” Bluestein told The Wausau Daily Herald in Wisconsin 2001. “There are schools, for instance, that close at certain wind-chill temperatures when perhaps they shouldn’t be closed.” The two scientists who developed the original system, Paul Siple and Charles Passel, based their research in the 1940s on a simple experiment: They hung water bottles from a pole on the roof of their research building and measured how quickly the water lost heat (or how quickly the water turned to ice). At the same time, they measured the surrounding air temperature and wind speed.
They found that the higher the wind speed, the faster the water froze. For people, that meant the windier it was, the faster they lost heat and the colder they felt.
Bluestein found numerous flaws with the experiment. The researchers had assumed that the temperature of human skin was 90 degrees Fahrenheit (it was closer to 50 degrees on a really cold day); they had placed the containers 33 feet above the ground, where wind speeds are higher (rather than the height of a person); and they took their measurements where it is far colder than where most people live. Bluestein ruminated over the problem for several years, until he went to a conference and met Randall Osczevski, a Canadian scientist, who had also been questioning the wind-chill formula.
The two began studying wind chill and wrote papers about their findings, drawing the attention of both the U.S. and Canadian governments in 2001. Soon they were enlisted by both countries to develop a new formula.
As part of the project they conducted a series of experiments with 12 people, male and female, measuring heat loss from the face in cold and wind as they walked on treadmills in a wind tunnel at different temperatures. A “wet trial” sprayed participants’ faces with a splash of water every 15 seconds to measure whether the presence of precipitation would make people feel colder. After plotting the data, they found that in some cases the original wind chill index was off by just a few degrees, but that the discrepancy grew at higher wind speeds. It confirmed what many meteorologists had already suspected: The old calculation had exaggerated.
Maurice Bluestein was born on Jan. 1, 1941, in the Bronx to immigrants from Poland.
He was accepted for admission by the City College of New York at 16 and earned his engineering degree in 1962. He received a master’s in mechanical engineering from New York University in 1964 and a Ph.D. in biomechanical engineering from Northwestern University in 1967.
He taught mechanical engineering at Indiana University-Purdue University Indianapolis for about 19 years.
Maurice Bluestein, shown at his desk in the 1960s, was a mechanical engineer whose work helped the Weather Service to gauge wind chill more accurately. Bluestein died on Aug. 28 at age 76.