Relative Humidity

Domain	Definitions
Aerospace	The (dimensionless) ratio of the actual vapor pressure of the air to the saturation vapor pressure. The corresponding ratios of specific humidity or of mixing ratio give approximations of sufficient accuracy for many purposes in meteorology. The relative humidity is usually express in percent. Also called humidity. See absolute humidity, dew point.The ratio of mixing ratio to saturation mixing ratio is preferred as a definition of relative humidity by the International Meteorological Organization.Symbol U. (references)
Archeological	The measure of moisture in the air in relation to the saturation point of the air at its current temperature. RH is measured as a percentage of the absolute humidity divided by the saturation humidity. (RH). (references)
Energy	A measure of the percent of moisture actually in the air compared with what would be in it if it were fully saturated at that temperature. When the air is fully saturated, its relative humidity is 100 percent. (references)
Environment	The ratio of the partial pressure of water to the saturation vapor pressure, also called saturation ratio; often expressed as a percentage. (references)
Geography	The ratio of the actual vapour pressure in a space at a given temperature, to the saturation pressure for the corresponding temperature. Source: European Union. (references)
	The ratio, generally expressed as a percent of the vapour pressure of water present in the atmosphere to that required for saturation at the same temperature. Source: European Union. (references)
Mining	The ratio, expressed as a percentage, of the amount of water vapor in a given volume of air to the amount that would be present if the air were saturated at the same temperature. CF:absolute humidity;specific humidity. (references)
Science	The ratio of the amount of water vapor in the air compared to the amount required for saturation (at a particular temperature and pressure). (references)
Solar	The amount of water vapor in the air expressed as the ratio between the measured amount and the maximum possible amount (the saturation point at which water condenses as dew). (references)
Weather	A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point. (references)
Source: compiled by the editor from various references; see credits.

Specialty Definition: Relative humidity

Relative humidity is the ratio of the current vapor pressure of the water vapor in the air (or another gas), to the vapor pressure at which the air will become saturated at its current temperature, usually expressed as a percentage. This is equal to the ratio of the current mass of water per volume of air, to the mass per volume for saturated air (the point at which dew or fog will form). Once fog forms, the droplets are considered liquid and no longer part of the gaseous air, which prevents the relative humidity from ever being above 100%.

For a given dewpoint or absolute humidity, the relative humidity will change inversely with the temperature. This is because moisture capacity increases with temperature – the principle behind everything from hair dryers to dehumidifiers. In the winter, this principle is also why the indoor humidity can be so low that it causes dry skin and itchy eyes, and large amounts of static electricity. Even if the outdoor humidity is at 100% (complete saturation), heating the air indoors causes the relative humidity of the indoor air to fall. With a lower relative humidity indoors, the moisture capacity of the air increases greatly. Likewise, the evaporation rate increases greatly.

Relative humidity is often mentioned in weather forecasts and reports, as it is an indicator of the likelihood of precipitation, dew, or fog. In hot summer weather, it also increases the apparent temperature to humans (and other animals), by preventing the evaporation of perspiration from the skin. This effect is calculated in a table, resulting in the heat index or humidex.

A device used to measure humidity is called a hygrometer, one used to regulate it is called a humidistat, or sometimes hygrostat. (These are analogous to a thermometer and thermostat for temperature, respectively.)

See also: heat index

Commercial Usage: Relative Humidity

Photo Album: Relative Humidity

Thumbnail	Description & Credit	Thumbnail	Description & Credit
	Large rawinsonde balloon is released in foreground It will measure atmospheric conditions during ascent. In the background are surface weather instruments. These measure temperature, relative humidity, pressure and precipitation. A mobile radar unit is also shown.Credit: National Severe Storms Laboratory (NSSL).		Rawinsonde weather balloon just after launch. Notice a parachute in the center of the string and a small instrument box at the end. After release it measures many parameters. These include temperature, relative humidity, pressure, and wind speed. This information is transmitted back to surface observers.Credit: National Severe Storms Laboratory (NSSL).
	Standard instrument shelter (called a Stevenson Screen) used by NSSL. Shelter houses temperature, pressure, and relative humidity instruments. Observer comes to shelter to take readings. The shelter is a wooden box painted white with double-louvered sides. It is mounted on a stand 4 feet above the ground.Credit: National Severe Storms Laboratory (NSSL).		A solar-powered Surface Automated Measurement (SAM) site. These are deployed to take measurements in and around severe weather. Tower instruments give wind direction and speed; rain gauge on left. White box houses temperature, relative humidity and pressure instruments.Credit: National Severe Storms Laboratory (NSSL).
	During the early 1980s, NSSL and University of Oklahoma researchers place TOTO (TOtable Tornado Observatory) in the path of an on-coming tornado. It would measure temperature, pressure, relative humidity etc. It would record the data on tape inside the 55 gallon drum. TOTO was hit by a small tornado only once in April, 1985.Credit: National Severe Storms Laboratory (NSSL).		Figure 37. Assman aspirating psychrometer, used to determine relative humidity by comparing dry and humid air temperatures. The instrument was designed on principles discovered by the German Ernst Ferdinand August, the director of the Gymnasium of Berlin, in 1825. Professor Richard Assman of the Meteorological Institute of Berlin, built this instrument about 1886.Credit: Sailing for Science - the NOAA Fleet Then and Now.
	Figure 38. Hygrometer register, built to record variations in relative humidity. The hygrometer is built on principles discovered by Horace Benedict Saussure in 1783 and uses the changes in length of human hair and animal hair with humidity to derive relative humidity. The exact age of this recording instrument is unknown.Credit: Sailing for Science - the NOAA Fleet Then and Now.
Source: compiled by the editor from various references; see credits.

Non-Fiction Usage: Relative Humidity

Frequency of Internet Keywords: Relative Humidity

Modern Translations: Relative Humidity

Language		Translations for "relative humidity"; alternative meanings/domain in parentheses.
Danish		relativ luftfugtighed (moisture content, relative air humidity), relativ fugtighedsgrad, relativ fugtighed (moisture content, relative air humidity). (various references)

Dutch		relatieve vochtigheit van lucht (moisture content, relative air humidity), relatieve vochtigheit (moisture content, relative air humidity), relatieve vochtigheid, vochtigheitsgraad (moisture content, relative air humidity), betrekkelijke vochtigheid. (various references)

Finnish		suhteellinen kosteus (moisture content, r.h., relative air humidity), suhteellinen ilmankosteus (moisture content, r.h., relative air humidity). (various references)

French		pression relative de vapeur (relative air humidity), humidite relative de l'air (relative air humidity), humidite relative (relative air humidity), humidité relative, HR,pour un rapport de mélange donné,l'humidité relative dépend de la température et de la pression atmosphérique,on l'exprime en pourcentage (relative air humidity), HR (Republic of Croatia), etat hygrometrique (relative air humidity), degre hygrometrique (relative air humidity), degré hygrométrique, état hygrométrique. (various references)

German		RLF, relativer Dampfdruck (moisture content, r.h., relative air humidity), relative Luftfeuchtigkeit (moisture content, r.h., relative air humidity, vapor pressure, vapour pressure, vapour tension), relative Luftfeuchte (moisture content, r.h., relative air humidity), relative Feuchtigkeit, relative Feuchte (moisture content, r.h., relative air humidity), Feuchtigkeitsgehalt (moisture content, moisture percentage, r.h., relative air humidity, water content). (various references)

Greek		σχετική υγρασία, υγρασία του αέρος (moisture content, r.h., relative air humidity). (various references)

Italian		umidit� relativa dell'aria (moisture content, r.h., relative air humidity), umidit� relativa (moisture content, r.h., relative air humidity). (various references)

Japanese Kanji		相対湿度 . (various references)

Japanese Katakana		そうたいしつど. (various references)

Pig Latin		elativeray umidityhay

Portuguese		humidade relativa do ar (moisture content, r.h., relative air humidity), humidade relativa (moisture content, r.h., relative air humidity), grau higrométrico (moisture content, r.h., relative air humidity), estado higrométrico (moisture content, r.h., relative air humidity). (various references)

Spanish		humedad relativa del aire (moisture content, r.h., relative air humidity), humedad relativa (moisture content, r.h., relative air humidity). (various references)

Swedish		relativ luftfuktighet (moisture content, r.h., relative air humidity), relativ fuktighet (moisture content, r.h., relative air humidity). (various references)

Turkish		bağıl nem. (various references)
Source: compiled by the editor from various translation references.

Misspellings: Relative Humidity

Anagrams: Relative Humidity

Alternative Orthography: Relative Humidity

Hexadecimal (or equivalents, 770AD-1900s) (references)

52 65 6C 61 74 69 76 65 48 75 6D 69 64 69 74 79

Leonardo da Vinci (1452-1519; backwards) (references)

Binary Code (1918-1938, probably earlier) (references)

01010010 01100101 01101100 01100001 01110100 01101001 01110110 01100101 00100000 01001000 01110101 01101101 01101001 01100100 01101001 01110100 01111001

HTML Code (1990) (references)

&#82 &#101 &#108 &#97 &#116 &#105 &#118 &#101 &#32 &#72 &#117 &#109 &#105 &#100 &#105 &#116 &#121

ISO 10646 (1991-1993) (references)

0052 0065 006C 0061 0074 0069 0076 0065 0048 0075 006D 0069 0064 0069 0074 0079

Encryption (beginner's substitution cypher): (references)

Domain	Title
Books	Tables of temperature, relative humidity, precipitation, and sunshine for the world (reference) (more book examples)
Source: compiled by the editor from various references; see credits.

Subject	Topic	Quote
Health		Seasonal changes in relative humidity also may affect the prevalence of colds. (references)
		Ixodes ticks can be found in temperate regions with high relative humidity at ground level. (references)
Source: compiled by the editor from ICON Group International, Inc.; see credits.

Expression	Frequency per Day
relative humidity	154
relative humidity chart	14
relative humidity sensor	12
relative humidity calculation	7
calculate relative humidity	6
relative humidity meter	5
relative humidity calculator	5
measuring relative humidity	3
temperature and relative humidity	3
relative humidity measurement	2
Source: compiled by the editor from various references; see credits.

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "a-d-e-e-h-i-i-i-l-m-r-t-t-u-v-y"
	-4 letters: meditatively.
	-5 letters: imitatively, iteratively, multitiered.
Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro.

Misspellings
	"Relative Humidity" is suggested in spellcheckers for the following: realative humidity, realtive humidity. (additional references)
Source: compiled by the editor, based on several corpora (additional references).

Relative Humidity

Definition: Relative Humidity