Charles Robert Darwin: b. 12 Feb, 1809 – d. 19 Apr, 1882
February 12th is Darwin Day. A day of celebration initiated by Darwin Day.org, a science education group, advocating the celebration of science- "our most reliable knowledge system."
Darwin Day 2009 also marks the 200th anniversary of Darwin's birthday.
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Click here (PDF) for a selection of articles, books, videos, and online resources about Darwin, natural selection, and evolution.
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Wednesday, January 28, 2009
Thursday, January 15, 2009
Whenever temperatures plummet television meteorologists warn of extreme wind chill.
But what is wind chill? Does it really get colder when the wind blows? Will wind chill freeze water? Can you get frostbite if the air temperature is above freezing? The answer to all of these questions is no.
We might feel colder when the wind blows because of heat loss due to evaporation and heat transfer from our skin to the air but wind chill is a subjective feeling or sensation of cold not an actual drop in air temperature. If you keep your exposed skin to a minimum and wear wind-blocking clothing then you should stay warm. It is this subjective feeling along with the increased risk of frostbite that wind chill attempts to approximate.
However, wind chill pronouncements by weather forecasters often are read with a finality they do not have. Wind chill depends not only on air temperature but wind speed and that can vary quite a bit. Saying the wind chill today is -17F is misleading because the wind and air temperature will vary throughout the day. What they are usually quoting is an average air temperature and wind speed. In other words, an approximate middle point for reference only rather than an absolute value.
So, when the weather person on the local TV news warns about negative wind chill it does not mean that the air temperature is that cold. It means that they want to, as Daniel Engber said, “put an exclamation point on the banality of winter.”
More Information & References
Ball State Information & Resources
- keywords: thermal equilibrium, radiative transfer, climate physics, climatology
- Call numbers: QA3, QC861.3
- keywords: frostbite, hypoxia, ischemic injury, reperfusion injury
- Call numbers: QH653, QH671, RB144.5
- "The truth about wind chill" & "Wind chill blows"by Daniel Engber
- "Can water freeze if the wind chill index is 10 degrees and the temperature is 35 degrees?" Dept. of Physics, Union University
- "Wind chill temperatures and charts" from the Internet Accuracy Project
- National Weather Service's wind chill index
- BSU weather station
- Cold stress, from the CDC
- Cold environments- health effects and first aid, from the Canadian Centre for Occupational Health and Safety
- "What is frostbite?" from NWS/NOAA FAQ
- Frostbite from the Mayo Clinic
- Frostbite from MedlinePlus.gov (NLM)
Research articles, etc.
- Eagan, C. (1964). Review of research on military problems in cold regions. C. Kolb and F. Holstrom eds. TDR-64-28. Arctic Aeromed. Lab. p 147–156.
- Osczevski, R. Wind chill: Whole body vs. facial cooling. DCIEM TR 2000-089, Nov. 2000
- Osczevski, Randall and Maurice Bluestein. The New Wind Chill Equivalent Temperature Chart. Bulletin of the American Meteorological Society, Oct. 2005, p. 1453–1458.
- Siple, Paul, quoted in: Cold Injury, 1958, Steven Horvath editor, Josiah Macy Foundation, p 216.
- Woodson, Wesley E. (1981). Human Factors Design Handbook, page 815. McGraw-Hill. ISBN 0-07-071765-6
- Tikuisis, P., and R. J. Osczevski (2002) Facial Cooling During Cold Air Exposure. Bull. Amer. Meteor. Soc. July 2003, p. 927–934