Wednesday, August 10, 2011

Limbaugh, Colbert, and feels like heat index

Steve Colbert did his best to defend the heat index. It was pretty funny. The video clip below contains an assault against thermodynamics - Steve Colbert does the very same thing as Sean Carroll except that the latter one isn't joking. ;-)

We learn that Rush Limbaugh, a part-time weather balloon, has complained about the heat index and the decision by some media to present it as a real temperature. The Big Government tries to make itself even bigger by announcing bigger temperatures.

While Colbert hopefully makes you laugh, the question posed by Limbaugh is serious. It is true that under normal circumstances, weather men focus on the temperature as measured by thermometers.

However, there is a big heat wave in the U.S. - something that we almost can't imagine here in Central Europe. And the weathermen suddenly switch to the "feels like" heat index and present it as a primary temperature.

The heat index - or "humiture" - is meant to be a higher number when it's hotter; and it's also higher when it's more humid. Why? Because if the relative humidity is higher, it's harder for your body to sweat and actually evaporate the sweat away - and to get rid of the excess heat. Aside from the humidity, there are other factors that could make you "feel" hotter.

For you to see that this concept is fashionable in America only, note that the Wikipedia article on the heat index only contains a complicated expansion in which everything is encoded in the Fahrenheit degrees.

The formula says
\[\begin{align}\mathrm{HI} &= c_1 + c_2 T + c_3 R + c_4 T R +\\ &+ c_5 T^2 + c_6 R^2 + c_7 T^2R + c_8 T R^2 + c_9 T^2 R^2\ \,\end{align}\] where \(c_i\) are constants, sometimes expressed at the relative accuracy of \(10^{-10}\) which is really insane.

If you realize that this is an ad hoc definition of a quantity that is meant to be subjective, this accuracy shows that the authors of the formula are detached from the reality.

When people use the "heat index" in the U.S., you may get much higher numbers. Instead of the temperature at 100 °F, people are told that the "feels like" temperatures are 120 °F. This may of course be done to mislead the people and exaggerate the actual heat wave by a modest increment of 20 degrees Fahrenheit.

Of course, there also exists a potentially legitimate explanation why the heat index becomes more popular when it's hot. The weather people may want to warn the people against the elevated risk of the extreme weather. For example, it's being said that when the heat index goes above 130 °F, heat stroke is imminent. Above 105 °F of "feels like" temperature, heatstroke is likely when you continue to work hard, and so on.

This story is somewhat arbitrary and contains guesses but it could suggest that the heat index is a legitimate format to describe the state of the atmosphere as relevant for the people. However, one must actually know at least much of the relevant theory above. Until very recently, I didn't know it.

And I am convinced that a vast majority of TV viewers don't really know what the "feels like" temperature means quantitatively and what are the consequences of various levels. How many Americans can say that "heatstroke is imminent above 130 °F"? Because of this ignorance, selling the "feels like" temperature as the real one to the generic viewers is really scam. The Americans want everything big but one should still carefully distinguish "big" and "small" conventions for expressing the temperature.

Extra links for the video at the top

The Colbert Report
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