NEW YORK — 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 – 35.75V0.16 + 0.4275TV0.16.
The result is the windchill 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 windchill 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 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 windchill formula, determined that with winds of about 15 miles per hour, 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, Dr. 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.’“
Dr. Bluestein had long been interested in how engineering could be applied to meet personal human needs. He worked on the Apollo space program to help create spacesuits that addressed waste management for NASA’s first moon landing. He worked for the Veterans Administration on designs for artificial limbs, and for Litton Medical Systems in its development of ultrasound imaging for detecting breast cancer.
This time, he set out to improve what he deemed an inaccurate, and alarmist, measurement for windchill.
“The old system scared people into taking unnecessary actions,” Dr. Bluestein told The Wausau Daily Herald in Wisconsin 2001. “There are schools, for instance, that close at certain windchill 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.
Dr. 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.
Dr. 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 windchill formula. Osczevski, an environmental physicist who worked for the Canadian defense department, had built a temperature-controlled artificial human head to monitor heat loss at a height of 5 feet, closer to the height of a typical human face, and had performed experiments at a military laboratory in Toronto. These focused on the face, because it is typically the most exposed part of the body on a winter day.
The two began studying windchill and wrote papers about their findings, drawing the attention of the US 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 windchill 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.
“We think people will now take it more seriously,” Dr. Bluestein said of windchill.
Maurice Bluestein was born 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 doctorate in biomechanical engineering from Northwestern University in 1967.
He taught mechanical engineering at Indiana University-Purdue University Indianapolis for about 19 years.
In addition to his daughter Karen, he leaves his wife, Maris; a son, Richard; another daughter, Jennifer; and two grandchildren.