From: JeffM@sanctum.com (Jeff Miller) Newsgroups: sci.math Subject: Re: Windchill function? Date: 28 Aug 1995 03:43:20 GMT In article , ishaq@plains.NoDak.edu says... > >Just looking for a function that, given windspeed and degrees F as input, >will compute windchill in degrees F. Any ideas? >thanks, The following is taken from _The Encyclopedia of Climatology_, edited by John E. Oliver and Rhodes W. Fairbridge (1987), although this entry was written by Thomas W. Schlatter. I've written T-sub-e for a T followed by the subscript e, etc. You'll be using the third formula. As a check, here is an entry from the accompanying chart: the wind chill equivalent temperature for a wind speed of 15 m/s and an air temperature of -12 degrees C should be -37 degrees C. Jeff Miller Gulf High School New Port Richey, FL The wind chill equivalent temperature T-sub-e, a fictitious temperature designed to account for the effect of wind on the sensation of cold, is often quoted when the weather is cold and windy. It is closely related to wind chill, the rate of heat loss per unit area of exposed skin. The defining equation is H-sub-o = (10.45 + (10 sqrt v-sub-o) - v-sub-o)(33 - T-sub-e), where H-sub-o is the wind chill (kilocalories per square meter per hour) than would occur if the wind speed were v-sub-o (m/s) and the air temperature were T-sub-e (degrees Celsius). The most often-used value of v-sub-o is 1.79 m/s (4 mph), about as fast as a person moves at a brisk walk. If v-sub-o is 1.79, then H-sub-o = 22.04 (33 - T-sub-e). The formula for the actual wind chill H is given above. By setting H = H-sub-o, one can solve for the wind chill equivalent temperature: T-sub-e = 33 - (10.45 + (10 sqrt v) - v)(33 - T)/22.04. This formula is not intended for use at wind speeds below 1.79 m/s, because it yields unreasonable results. ============================================================================== From: folsomman@aol.com (FolsomMan) Newsgroups: sci.math Subject: Re: Windchill function? Date: 27 Aug 1995 23:51:23 -0400 ishaq@plains.NoDak.edu (Jeffro) wrote: >Just looking for a function that, given windspeed and degrees F as input, >will compute windchill in degrees F. Any ideas? As I recall, windchill was derived from an experiment where the freezing time was measured for plastic bags filled with water at different wind speeds and ambient conditions. Calculation of these results requires that you find the film heat transfer coefficient for air at the ambient conditions. No one can do this at present from first principles without a supercomputer (nor is anyone likely to soon). The are tables and graphs of the Nusselt Modulus, and other relevant dimensionless parameters used in empirical analysis of these kinds of problems, available in various heat transfer references. It isn't a simple problem, since there are discontinuities where air flow changes from laminar to turbulent. Good luck. Mark Folsom ==============================================================================