Education Journalist | Study Abroad Lead
Heat Index can be defined as an index that combines air temperature and relative humidity, in shaded areas, in order to pose a human-perceived equivalent temperature, as to how it would feel if the humidity were some other value in the shade. Basically, the heat index is a thermodynamic value that relates to air temperature and humidity. The human body usually cools itself down through perspiration or sweating. We know that the Heat is removed from the body when the sweat evaporates. However, high relative humidity reduces the evaporation rate, resulting in a lower heat removal rate from the body, causing the sensation of being overheated. It is the humidity and not heat.
| Table of Content |
Key Terms: Heat Index, Temperature, Relative Humidity, Heat, Perspiration, Evaporation, Human Body
What is Heat Index?
[Click Here for Sample Questions]
The heat index is an index that combines the temperature of air and relative humidity. In shaded areas, to propose a human-perceived equivalent temperature, as to how hot it would feel if the humidity were a different value in the shade. Since the heat index is based on temperatures in the shade, while people usually move across sunny areas, the heat index can give a much lower temperature than the actual conditions of typical outdoor activities.
Example: When the temperature is given as 32°C with 70% relative humidity, the heat index would be 41°C. The given heat index has an implied humidity of 20%. Basically, it is the value of the relative humidity for which the heat index formula shows 41°C. A heat index temperature of 32°C holds or carries an implied relative humidity of 38%.
Heat Index
Read More: Density of Air
Heat Index Formula
[Click Here for Sample Questions]
The heat index formula is given as follows:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
Where,
- HI = Heat Index in Degrees Fahrenheit
- T = Temperature in Degrees Fahrenheit
- R = Relative Humidity
- c1- c9= Constants
- c1 = -42.379
- c2= -2.04901523
- c3 = -10.14333127
- c4 = -0.22475541
- c5 = -6.83783 x 10-3
- c6 = -5.481717 x 10-2
- c7 = -1.22874 x 10-3
- c8 = 8.5282 x 10-4
- c9 = -1.99 x 10-6
Read More: Unit of Humidity
Uses of Heat Index
[Click Here for Sample Questions]
- Heat index is used to approximate the human body’s perception of the humidity and heat in order to create healthy or public plans that can cultivate human and animal safety.
- The areas that are exposed to sunlight could have a higher or lower heat index.
- People doing different activities can perceive heat differently and not really feel the heat index as per calculation for that day or place.
Things to Remember
- The heat index is an index that combines the temperature of air and relative humidity.
- In shaded areas, propose a human-perceived equivalent temperature, as to how hot it would feel if the humidity were a different value in the shade.
- The human body usually cools itself down by perspiration or sweating. Heat is removed when the sweat evaporates from our bodies.
- Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
- The heat index was created to help better display the dangers of excessive heat on the human body and relay how hot the current weather conditions are making it feel to the average person.
Read More: Distinguish between Weather and Climate
Sample Questions
Ques. Calculate HI for a temperature of 185°F and 86%. Use Heat Index Formula. (3 Marks)
Ans. Given: R=86%
T= 185°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 185 + – 10.14333127 86 + – 0.22475541 185 86 + – 6.8378310-3(185)2 + – 5.481717 x 10-2 (86)2 + – 1.22874 10-3(185)2 86 + 8.5282 10-4 185 (86)2 + – 1.99 10-6(185)2 (86)2
So, Heat Index is 1274°F.
Ques. Determine the heat index if the temperature is 190°F and the relative humidity is 80%. (3 Marks)
Ans. Given: R=80%
T= 190°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 190 + – 10.14333127 80 + – 0.22475541 190 80 + – 6.8378310-3(190)2 + – 5.481717 x 10-2 (80)2 + – 1.22874 10-3(190)2 80 + 8.5282 10-4 190 (80)2 + – 1.99 10-6(190)2 (80)2
So, the heat index is 1270°F.
Ques. Determine heat index for the relative humidity of 86% and the temperature of 197°F. (3 Marks)
Ans. Given: R=86%
T= 197°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 7 + – 10.14333127 86 + – 0.22475541 197 86 + – 6.8378310-3(197)2 + – 5.481717 x 10-2 (86)2 + – 1.22874 10-3 (197)2 86 + 8.5282 10-4 197 (86)2 + – 1.99 10-6 (197)2 (86)2
So, the heat index is 1527°F.
Ques. Calculate HI for a temperature of 172°F and 78%. Use Heat Index Formula. (3 Marks)
Ans. Given: R=78%
T= 172°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 172 + – 10.14333127 78 + – 0.22475541 172 78 + – 6.8378310-3(172) 2 + – 5.481717 x 10-2 (78)2 + – 1.22874 10-3 (172)2 78 + 8.5282 10-4 172 (78)2 + – 1.99 10-6(172)2 (78)2
So, Heat Index is 919°F.
Ques. Calculate HI for a temperature of 160°F and 70%. Use Heat Index Formula. (3 Marks)
Ans. Given: R=70%
T= 160°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 160 + – 10.14333127 70 + – 0.22475541 160 70 + – 6.8378310-3(160)2 + – 5.481717 x 10-2 (70)2 + – 1.22874 10-3(160)2 70 + 8.5282 10-4 160 (70)2 + – 1.99 10-6(160)2 (70)2
So, Heat Index is 655°F.
Ques. Calculate HI for a temperature of 192°F and 80%. Use Heat Index Formula. (3 Marks)
Ans. Given: R=80%
T= 192°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 192 + – 10.14333127 80 + – 0.22475541 192 80 + – 6.8378310-3(192)2 + – 5.481717 x 10-2 (80)2 + – 1.22874 10-3 (192)2 80 + 8.5282 10-4 192 (80)2 + – 1.99 10-6 (192)2 (80)2
So, Heat Index is 1309°F.
Ques. Determine heat index for the relative humidity of 88% and the temperature of 195°F. (3 Marks)
Ans. Given: R=88%
T= 195°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 195 + -10.14333127 88 + – 0.22475541 195 88 + – 6.8378310-3(195)2 + – 5.481717 x 10-2 (88)2 + – 1.22874 10-3(195)2 88 + 8.5282 10-4 195 (88)2 + – 1.99 10-6(195)2 (88)2
So, Heat Index is 1521°F.
Ques. Determine heat index for the relative humidity of 90% and the temperature of 185°F. (3 Marks)
Ans. Given: R=90%
T= 185°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 185 + – 10.14333127 90 + – 0.22475541 185 90 + – 6.8378310-3(185)2 + – 5.481717 x 10-2 (90)2 + - 1.22874 10-3(185)2 90 + 8.5282 10-4 185 (90)2 + -1.99 10-6(185)2 (90)2
So, Heat Index is 1340°F.
Ques. Calculate HI for a temperature of 190°F and 82%. Use Heat Index Formula. (3 Marks)
Ans. Given: R=82%
T= 190°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 4 2.379 + – 2.04901523 190 + – 10.14333127 82 + – 0.22475541 190 82 + – 6.8378310-3(190)2 + – 5.481717 x 10-2 (82)2 + - 1.22874 10-3(190)2 82 + 8.5282 10-4 190 (82)2 + – 1.99 10-6(190)2 (82)2
So, Heat Index is 1305°F.
Ques. Calculate HI for a temperature of 170°F and 90%. Use Heat Index Formula. (3 Marks)
Ans. Given: R=90%
T= 170°F
By using the formula we get:
Heat Index (HI) = c1 + c2T + c3R + c4TR + c5T2+ c6R2 + c7T2R + c8TR2+ c9T2R2
HI = – 42.379 + – 2.04901523 170 + – 10.14333127 90 + – 0.22475541 170 90 + – 6.8378310-3(170)2+ -5.481717 x 10-2 (90)2 + – 1.22874 10-3(170)2 90 + 8.5282 10-4 170 (90)2 + – 1.99 10-6(170)2 (90)2
So, Heat Index is 1042°F.
Also Read:
Also Read:
Comments