## Monday, 11 March 2013

### Wind chill

Blimey o' Riley its cold, really cold. It's that windchill factor that the weathermen keep talking about. Today was about 0 degrees C but with the wind chill factor it 'felt like' -6 degrees.

Today that wind really is bitter and it is the wind that really makes the difference.

The body is at a temperature of 37 degrees and usually, well always in the UK, the temperature is below that. This means that the human body will lose heat to the environment wherever there is exposed skin. Heat is lost in three ways, conduction, convection and radiation. As the heat is lost it warms up a layer of air above the skin. If this air remains in place it acts as a insulating blanket making it harder for more heat to be lost.

However, when a wind is blowing this warmed up air is being continually removed thus maintaining a large temperature gradient allowing heat to be lost more rapidly. This makes the homeostatic mechanisms of the body respond, causing shivering, vasoconstriction, a desire to wear warm clothes and goose pimples and a feeling of cold.

There is even a equation for working it all out:

Twc = 13.12 + 0.6215Ta - 11.37V(+0.16) + 0.3965TaV(+0.16)

where $T_{\rm wc}\,\!$ is the wind chill index, based on the Celsius temperature scale, $T_{\rm a}\,\!$ is the air temperature in degrees Celsius (°C), and $V\,\!$ is the wind speed at 10 metres (standard anemometer height), in kilometres per hour (km/h).

All I know is its really quite cold.