It’s that time of the year here in Pittsburgh, when I start cursing the first human who moved north of the tropic of Cancer from the bottom of my heart. For, once again, it takes me 10 minutes from when I’m “ready to leave” to when I actually leave the house after putting on many layers of socks, boots, half a dozen sweaters and coats, a couple of scarves, a hat and, of course, two pairs of gloves. (Whew! It was exhausting just typing all that!)
It’s not the actual below-freezing temperatures which get to me, mind you. It’s the wind – the terrible wind which whistles through the little holes in your hat and freezes your ears, finds the little spot of skin that you forgot to cover up and turns it into ice as you wait for the bus in the morning.
You might’ve noticed this too: some days the temperature might read 0 degrees and it feels like you’re living in the Tundra and on other days – especially those days when it’s sunny outside and there is not a whiff of wind in sight – 0 degrees is quite manageable! Which is why, when I check the weather in the morning, I pay little attention to the temperature listed; my eye automatically goes to the “feels like” temperature or “wind chill factor” given by the weather channels. Of course, what the weather “feels like” varies from person to person and is also affected by factors such as how long you stay outside, whether you’re standing in the sun or the shade, and what you’re wearing. The wind chill factor is just a way to quantify the terrible cold and to give you something to substantiate your claim when you say “OMG! It felt like -40 degrees outside!”.
Turns out the wind is more evil than we thought. Our body constantly generates heat, which gets transferred to the air molecules surrounding our body. When the wind blows, it steals these warm air molecules away from our immediate surroundings, causing us to generate more heat to warm up the air that replaces it – which makes us feel colder. It’s akin to when you blow on your steaming cup of coffee to get it to be slightly cooler so you can actually drink it. Every time you blow on it, the heat from the top of the beverage is transferred to the air you’re blowing, and the beverage loses a little bit more heat.
A way to quantify this effect was originally concocted in the 1930s, by two men (Paul Siple and Charles F. Passel) who were working in Antarctica. They filled plastic containers with water and hung them from a pole outside their window. Every day, they measured the temperature outside, the speed of the wind, and the rate at which the water in the container turned to ice, and came up with an equation to measure the effect of wind on the temperature. Weathermen started using this to report “feels like” temperatures in the 1970s. However, there were soon noticeable inconsistencies, such as how “feels like” -40 degree weather with wind seemed to be more manageable than “feels like” -40 degree weather without wind. It was soon discovered that these researchers had over-estimated the effect of the wind chill.
National weather agencies became worried that this over-estimation could lull people into a false sense of how cold it really is. For example, suppose the weather agency reports a miscalculated “feels like” temperature of -35 degrees instead of the correct “feels like” temperature of, say, -20 degrees. Everyone will prepare for a really cold day and bundle up, but to their surprise, it’s not as bad as they feared. These ordinary citizens now have a misconception about how to dress for -35 degrees – a misconception that could prove to be dangerous. If, at a later time, the thermometer really drops to -35 degrees but there is no wind, everyone will dress as though it’s -20 degree weather. Conceivably, this could be quite dangerous and maybe even fatal!
In order to stop misleading people, US, Canada and UK devised a new experiment in 2001 to re-evaluate how the wind chill factor is calculated. Twelve volunteers donned winter coats and walked on a treadmill inside a wind tunnel. Their internal temperature was measured using a rectal thermometer, and a small probe measured the skin temperature at their nose, forehead, cheeks and ears. They walked for 90 minutes at three different temperatures: 50oF (+10oC), 32oF (0oC), and 14oF(-10oC) when the wind was blowing at 4.5, 11 or 18 mph (7.2, 17.7, or 29 km/h)
Based on the measurements made, they came up with the following formula:
Tfeels like = 13.12 + 0.6215 * T0 – 11.37 * V +0.16 + 0.3965 * T0 * V+0.16,
where V is the wind speed and T0 is the temperature as seen on the thermometer. What this equation tells us is that the difference between actual temperature and “feels-like” temperature increases proportionally with increasing wind speed. Today, this is the formula used by the weather agencies to calculate the little number that appears on your phone.
Of course, knowing how the wind chill is calculated does not help me as I shiver my way to school in the morning, but at least now I know how prepared I need to be. Then again, does any amount of preparation help one survive Pittsburgh winters? I guess I should just be glad I don’t live in Oymyakon for now!