Tuesday, April 04, 2006

Wind chill and springing forward

I haven't done this in a while, but my children have asked me some quesitons, and I want to answer them.

What is the wind chill index? Well we all know what the wind chill index is. It is how much colder the wind makes us feel on a cold day.
Anyone who has ever waited at a bus stop or taken a walk on a blustery winter day knows that you feel colder when the wind blows. We call the cooling sensation caused by the combined effect of temperature and wind the wind chill.

On a calm day, our bodies insulate us somewhat from the outside temperature by warming up a thin layer of air close to our skin, known as the boundary layer. When the wind blows, it takes this protective layer away-exposing our skin to the outside air. It takes energy for our bodies to warm up a new layer, and if each one keeps getting blown away, our skin temperature will drop, and we will feel colder.

Wind also makes you feel colder by evaporating any moisture on your skin-a process that draws more heat away from your body. Studies show that when your skin is wet, it loses heat much faster than when it is dry.

But how is/was it determined? This is where things get a little interesting ....
The original wind chill formula was derived from experiments conducted in 1939 by Antarctic explorers, Paul Siple and Charles Passel. These hardy scientists measured how long it took for water to freeze in a small plastic cylinder when it was placed outside in the wind. Over the years, the formula was modified somewhat, but remained based on the Antarctic experiments.

However, there was a need for an adjustment and Canada led the way
The new index is based on the loss of heat from the face-the part of the body that is most exposed to severe winter weather. Volunteers were exposed to a variety of temperatures and wind speeds inside a refrigerated wind tunnel. They were dressed in winter clothing, with only their faces exposed directly to the cold. To simulate other factors affecting heat loss, they also walked on treadmills and were tested with both dry and wet faces.

Though the previous answer is hardly appropriate when the spring has sprung, the next one is quite timely. Why does daylight savings time officially start at 2 am? The answer, it appears, is practical
In the U.S., 2:00 a.m. was originally chosen as the changeover time because it was practical and minimized disruption. Most people were at home and this was the time when the fewest trains were running. It is late enough to minimally affect bars and restaurants, and it prevents the day from switching to yesterday, which would be confusing. It is early enough that the entire continental U.S. switches by daybreak, and the changeover occurs before most early shift workers and early churchgoers (particularly on Easter) are affected.

Technorati tags: , .

No comments: