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The representation is made on a temperature-relative humidity, instead of a standard psychrometric chart. The comfort zone in blue represents the 90% of acceptability, which means the conditions between -0.5 and +0.5 PMV, or PPD < 10%.
When the temperature is 30 °C (86 °F) and the dew point is 15 °C (59 °F), the humidex is 34. If the temperature remains 30 °C (86 °F) and the dew point rises to 25 °C (77 °F), the humidex rises to 42. The humidex is higher than the U.S. heat index at equal temperature and relative humidity. The humidex formula is as follows: [7] [8]
In hot summer weather, a rise in relative humidity increases the apparent temperature to humans (and other animals) by hindering the evaporation of perspiration from the skin. For example, according to the heat index, a relative humidity of 75% at air temperature of 80.0 °F (26.7 °C) would feel like 83.6 ± 1.3 °F (28.7 ± 0.7 °C). [13] [14]
The wet-bulb globe temperature (WBGT) is a measure of environmental heat as it affects humans. Unlike a simple temperature measurement, WBGT accounts for all four major environmental heat factors: air temperature, humidity, radiant heat (from sunlight or sources such as furnaces), and air movement (wind or ventilation). [ 1 ]
Apparent temperature, also known as "feels like", [1] [2] is the temperature equivalent perceived by humans, caused by the combined effects of air temperature, relative humidity and wind speed. The measure is most commonly applied to the perceived outdoor temperature.
A lower dew point depression indicates that the air is more moist at a given temperature. [1]: 83 For a constant temperature, the smaller the difference, the more moisture there is, and the higher the relative humidity.
Alternatively, the cloud base can be estimated from surface measurements of air temperature and humidity by calculating the lifted condensation level. One method for doing this, used by the U.S. Federal Aviation Administration and often named after Tom Bradbury, [1] is as follows: Find the difference between the surface temperature and the dew ...
Thornthwaite developed four indices: the Moisture Index (Im), the aridity and humidity indexes (Ia/Ih), the Thermal Efficiency Index (TE) and the Summer Concentration of Thermal Efficiency (SCTE). Each of the four climatic types can be described by an English alphabet letter and are arranged exactly by the order shown previously. [5]