The wind is chilling today! We may have heard this sentence several times during winters. But do we actually know what does this mean? Wind chill is basically the decrease in the temperature which is felt by our body because of the flow of air. It is also called as real feel temperature or feels like in many countries. Wind-chill is the perceived decrease in air temperature felt by the body on exposed skin due to the flow of air. The effect of wind chill is to increase the rate of heat loss and reduce any warmer objects to the prevailing temperature at a faster rate. It cannot, however, reduce the temperature of these objects below its present temperature, no matter how high the wind velocity is. In simple terms, the air 'feels' colder than it is. This happens due to the chilling effect of the wind on our skin. When the conditions are extreme, it increases the risk of developing frostbites.
Wind chill numbers are usually lower than the air temperature for values where the formula is valid.
The formula for calculating wind chill factor is as follows:-
Twc = 13.2 + 0.621T – 11.37V0.16 + .3965TV0.16
Twc = the wind chill index in °C.
V = Air Speed in kmph
Wind chill is defined only for temperature less than 10°C (50°F) and wind speed above 5 kmph (about 3.0 mph). As the air temperature falls, the effect of wind chill increases, e.g. a 20 kmph wind will lower the feel like temperature by a bigger margin, at -20°C than the same wind speed at -10°C meaning lower the temperature greater the wind chill.
The method for calculating the wind has always attracted controversy as meteorologists have varied opinion on whether to consider the exposed skin area like face or full body or to consider naked body or wearing appropriate clothing.
In a study conducted in India over 41 districts, it was found that only in a few districts of Northern India, the climatology of Wind chill factor is less than 10°C. The value is less than 5°C mainly in winter’s i.e.in the months of January and February and in the post monsoon period i.e. in the months of October and November. The number of days with Twc < 10°C during winter and post monsoon are given in the table below.
Extreme case
On July 2003, an extreme record of wind chill was observed. The Remote Weather Station in East Antarctica recorded a temperature of -94°F which was pretty cold in itself but add to it a wind howling at 75 mph & you have got a wind chill factor of -150°F or -660C.!!
