den@parallel.UUCP (Dennis Briscoe) (08/02/84)
Can anyone tell me how wind chill factors are calculated? I often hear television and radio announcers talk about how cold it is at a football game, etc. "The temperature is 12 degrees fahrenheit with the wind chill factor making it -20 degrees." With just a little thought one realizes that it isn't likely that air at 12 degrees could cool an object down to -20 degrees. It won't likely cause a pond to freeze, for instance. There could be some cooling due to faster evaporation, but is the wind chill factor dependent on the humidity of the air and the surface moisture of the object in question? When I discussed this question with another person at work some time ago, he said that since the body warms the air around it, thermal layers of air form. These layers are stripped off by the wind. This makes a lot of sense to me, but it still means that the wind chill factor is dependent on the amount of heat transferred from the body (or from any object whose tem- perature is higher than ambient). The internal temperature and the type of insulation on a person or other object would make a big difference. In the "12 degrees / -20 degrees" example, if a block of ice were on the field, it would melt faster than it would with no wind at 12 degrees, and of course at -20 degrees it wouldn't melt at all. Perhaps wind chill factor is only supposed to be a rough guideline for adjusting calculations for probable survival time in the wilderness. Many of the questions still apply, and as I have mentioned, it is often used in other contexts. So, my questions are, "How is wind chill factor calculated?", "Is it scien- tifically valid?", "Does it apply only to humans?", and "What assumptions are made about clothing, etc.?" Einstein didn't know beans, (but that's another story) Dennis Briscoe - - Parallel Computers
ward@hao.UUCP (Mike Ward) (08/04/84)
[] Whatever the scientific merits of wind chill factor, and however it is supposed to be calculated, there is one thing for certain: the news media will follow the prime rule of the News Media: (herein expained by use of it in context) in matters requiring understanding of the subject matter, THEY DON'T GET IT! In matters requiring accuracy, THEY DON'T GET IT! In matters requiring honesty, THEY DON'T GOT IT! > Einstein didn't know beans, > (but that's another story) Yeah, but Einstein didn't talk about beans. -- Michael Ward, NCAR/SCD UUCP: {hplabs,nbires,brl-bmd,seismo,menlo70,stcvax}!hao!sa!ward ARPA: hplabs!hao!sa!ward@Berkeley BELL: 303-497-1252 USPS: POB 3000, Boulder, CO 80307
jpl@allegra.UUCP (John P. Linderman) (08/05/84)
Here's a formula I pulled out of the New York Times a few years ago.
I can't vouch for its accuracy. The sign change at high velocities
is disturbing in the abstract, but since the reversal occurs around
100 meters per second (223 miles per hour) the formula may well be
correct for conditions most of us will experience. [In a 220 mph
wind, frostbite is probably less of a concern than where you will
come down.]
v = wind velocity in meters / second
t = temperature in degrees Celcius
skin temperature is approximately 33 degrees C
heat loss in kilocalories / square meter is
1/2
( 10 * v + 10.45 - v ) * ( 33 - t )
John P. Linderman Department of Obscure Formulae allegra!jplrieka@ames.UUCP (Rieka E. McCain) (08/14/84)
I remember reading a book about Little America (the one at the South Pole, not the town in Wyoming) in which the scientists there, some time in the fifties, empirically derived the wind chill charts and extrapolated the values on out past the point at which the subject would have suffered irrepairable injury (unlike the German WWII experiments on survival time of downed fliers). If anyone is really interested in the subject (now is the time to get those winter survival skills together- before snow falls), I would suggest getting a copy of Mountaineering Medicine or Mountaineering, the freedom of the Hills or hitting up the National Ski Patrol for a copy of the Winter Mount- aineering Handbook. Best of all, Signup for a NSPS winter Mountaineering course and you get a chance to practice what you learn. (survival in the mountains is too important to be left to "I remember reading...") Notice: I am not necessarily advocating that you JOIN the NSPS, as part of their public service type stuff they offer the course to anyone. Even paid professional ski-patrollers and mountaineering guides take their courses... . w . ZZ T a d.