Liberal Arts Blog — What Exactly Is the Heat Index? Why Does It Matter? How Is It Calculated?
Liberal Arts Blog — Monday is the Joy of Math, Statistics, Shapes, and Numbers Day
Today’s Topic: What Exactly Is the Heat Index? Why Does It Matter? How Is It Calculated?
The gist of it: “When the body gets too hot, it begins to perspire or sweat to cool itself off. If the perspiration is not able to evaporate, the body cannot regulate its temperature. Evaporation is a cooling process. When perspiration is evaporated off the body, it effectively reduces the body’s temperature. When the atmospheric moisture content (i.e. relative humidity) is high, the rate of evaporation from the body decreases. In other words, the human body feels warmer in humid conditions. The opposite is true when the relative humidity decreases because the rate of perspiration increases. The body actually feels cooler in arid conditions.” Now, for a few more details. Experts — please chime in. Correct, elaborate, elucidate.
WHAT MANY DON’T KNOW — THESE NUMBERS ARE FOR SHADY LOCATIONS!!!!
1. “If you are exposed to direct sunlight, the heat index value can be increased by up to 15°F.”
2. “As shown in the table below, heat indices meeting or exceeding 103°F can lead to dangerous heat disorders with prolonged exposure and/or physical activity in the heat.”
THE ROUGH EQUATION: Heat Index = -42.379 + 2.04901523T + 10.14333127R — 0.22475541TR - 6.83783 x 10–3T2–5.481717 x 10–2R2 + 1.22874 x 10–3T2R + 8.5282 x 10–4TR2–1.99 x 10–6T2R2
1. “If you’re really mathematically inclined, there is an equation that gives a very close approximation to the heat index.”
2. “However, this equation was obtained using a multiple regression analysis, and therefore, it has an error of ±1.3°F.”
3. T — air temperature (F) and R — relative humidity (percentage)
A LITTLE BIT OF HISTORY, THE CANADIAN COMPARISON, SYNONYMS, DETAILS
1. “The heat index was developed in 1979 by Robert G. Steadman. Like the wind chill index, the heat index contains assumptions about the human body mass and height, clothing, amount of physical activity, individual heat tolerance, sunlight and ultraviolet radiation exposure, and the wind speed. Significant deviations from these will result in heat index values which do not accurately reflect the perceived temperature.”
2.“In Canada the similar humidex (a Canadian innovation introduced in 1965) is used in place of the heat index. While both the humidex and the heat index are calculated using dew point, the humidex uses a dew point of 7 °C (45 °F) as a base, whereas the heat index uses a dew point base of 14 °C (57 °F). Further, the heat index uses heat balance equations which account for many variables other than vapor pressure, which is used exclusively in the humidex calculation. A joint committee formed by the United States and Canada to resolve differences has since been disbanded.”
3. Synonyms: “apparent temperature,” “feels like,” “felt air temperature,” “real feel.”
NB: “This effect is subjective, with different individuals perceiving heat differently for various reasons (such as differences in body shape, metabolic differences, differences in hydration, pregnancy, menopause, effects of drugs or drug withdrawal, its measurement has been based on subjective descriptions of how hot subjects feel for a given temperature and humidity.”
#2 “39 Songs, Prayers, and Poems: the Keys to the Hearts of Seven Billion People” — Adams House Senior Common Room Presentation, 11/17/20
Last four years of posts organized thematically:
Please share the coolest thing you learned this week related to math, statistics, or numbers in general. Or, even better, the coolest or most important thing you learned in your life related to math.
This is your chance to make someone else’s day. And to consolidate in your memory something you might otherwise forget. Or to think more deeply than otherwise about something dear to your heart. Continuity is key to depth of thought.