The notion of air "holding" water vapor or being "saturated" by it is often mentioned in connection with the concept of relative humidity. This effect can be calculated using a heat index table, also known as a humidex.
#Humidity and dew point skin#
For animal life dependent on perspiration (sweating) to regulate internal body temperature, high humidity impairs heat exchange efficiency by reducing the rate of moisture evaporation from skin surfaces. Humidity plays an important role for surface life.
Specific humidity is the ratio of water vapor mass to total moist air parcel mass. Relative humidity, often expressed as a percentage, indicates a present state of absolute humidity relative to a maximum humidity given the same temperature. Absolute humidity is expressed as either mass of water vapor per volume of moist air (in grams per cubic meter) or as mass of water vapor per mass of dry air (usually in grams per kilogram). Three primary measurements of humidity are widely employed: absolute, relative, and specific. For example, a parcel of air near saturation may contain 28 g of water per cubic metre of air at 30 ☌ (86 ☏), but only 8 g of water per cubic metre of air at 8 ☌ (46 ☏). The amount of water vapor contained within a parcel of air can vary significantly. As the temperature of a parcel of air decreases it will eventually reach the saturation point without adding or losing water mass. The amount of water vapor needed to achieve saturation increases as the temperature increases. The same amount of water vapor results in higher relative humidity in cool air than warm air. Humidity depends on the temperature and pressure of the system of interest. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Water vapor, the gaseous state of water, is generally invisible to the human eye.
Humidity is the concentration of water vapor present in the air. Global distribution of relative humidity at the surface averaged over the years 1981–2010 from the CHELSA-BIOCLIM+ data set
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