Re: wind chill

Re: wind chill

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Posted by Elena Shevliakova on September 16, 1997 at 16:50:44:
In Reply to: wind chill posted by shane frederick on September 16, 1997 at 15:14:29:
: What does wind chill mean?
According to The encyclopedia of Climate and Weather, the concept of wind chill was fist defined by Paule A. Siple to describe variations in human comfort caused by wind at cold temperatures. He defined wind chill as the measure of quantity of heat that atmosphere is capable of absorbing within an hour from an exposed surface one meter square. Siple studied wind chill in the experiments in Antarctica in which he measured freezing RATE of water at various wind speeds and temperatures.
: For example consider the following two locations:
: Location A Ambient temperature = -10 Wind Chill = -50
: Location B Ambient temperature = -50 Wind Chill = -50 (Calm)
: If you stuck a big block of 100 degree aluminum outside in these two locations,
: would it cool to 100 - X degrees in the same amount of time at both location?
If you leave both blocks outside long enough they both will reach temperature of their ambient environments, -10°C and -50°C respectively. Although, rates of heat loss will be different, because different initial temperatures between the blocks and their environments and absence/presence of wind.
: Does it matter what the intial temperature of the body is, what it is composed of?
The difference between the block temperature and air temperature matters. Material makes a big difference. Materials differ one from another in their heat capacity and in their thermal conductivities.
: Does a wind chill temperature really "feel" as cold in both locations. Is there
: any psychophysical evidence of this, or are the wind chill
: formulas based on some physical test, like the one described above?
Wind chill characterizes the rate of heat transfer to the atmosphere from a body. A person will experience physiologically different rates of heat lost with and without wind at the smae temperature.
: (3) Is it true that beyond a certain wind speed (like 70 mph), stronger winds actually begin to impart thermal energy to the body, and thereby reverse the "wind chill" effect?
: (4) Can you freeze water by blowing dry air over it quickly, even if the ambient temperature of the air exceeds 0.

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: : What does wind chill mean? : According to The encyclopedia of Climate and Weather, the concept of wind chill was fist defined by Paule A. Siple to describe variations in human comfort caused by wind at cold temperatures. He defined wind chill as the measure of quantity of heat that atmosphere is capable of absorbing within an hour from an exposed surface one meter square. Siple studied wind chill in the experiments in Antarctica in which he measured freezing RATE of water at various wind speeds and temperatures. : : For example consider the following two locations: : : Location A Ambient temperature = -10 Wind Chill = -50 : : Location B Ambient temperature = -50 Wind Chill = -50 (Calm) : : If you stuck a big block of 100 degree aluminum outside in these two locations, : : would it cool to 100 - X degrees in the same amount of time at both location? : If you leave both blocks outside long enough they both will reach temperature of their ambient environments, -10°C and -50°C respectively. Although, rates of heat loss will be different, because different initial temperatures between the blocks and their environments and absence/presence of wind. : : Does it matter what the intial temperature of the body is, what it is composed of? : The difference between the block temperature and air temperature matters. Material makes a big difference. Materials differ one from another in their heat capacity and in their thermal conductivities. : : Does a wind chill temperature really "feel" as cold in both locations. Is there : : any psychophysical evidence of this, or are the wind chill : : formulas based on some physical test, like the one described above? : Wind chill characterizes the rate of heat transfer to the atmosphere from a body. A person will experience physiologically different rates of heat lost with and without wind at the smae temperature. : : (3) Is it true that beyond a certain wind speed (like 70 mph), stronger winds actually begin to impart thermal energy to the body, and thereby reverse the "wind chill" effect? : : (4) Can you freeze water by blowing dry air over it quickly, even if the ambient temperature of the air exceeds 0.
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