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[ 0 => '{{short description|Gaseous phase of water}}', 1 => '{{Use mdy dates|date=October 2015}}', 2 => '{| class="infobox" cellspacing="0" cellpadding="2"', 3 => '! {{Chemical datatable header}}| Water vapor (H₂O)', 4 => '|-', 5 => '| colspan="2" style="text-align:center;"| [[File:St Johns Fog.jpg|200px]]<br />{{longitem|Invisible water vapor condenses to form<br />visible [[cloud]]s of liquid rain droplets|style=padding: 5px 0; line-height: 1.4em; text-align: center;}}', 6 => '|-', 7 => '| [[Liquid state]]', 8 => '| [[Properties of Water|Water]]', 9 => '|-', 10 => '| Solid state', 11 => '| [[Ice]]', 12 => '|-', 13 => '! {{Chemical datatable header}}| Properties<ref>{{harvp|Lide|1992}}</ref>', 14 => '|-', 15 => '| [[Chemical formula|Molecular formula]]', 16 => '| H₂O', 17 => '|-', 18 => '| [[Molar mass]]', 19 => '| 18.01528(33)&nbsp;[[Gram|g]]/[[Mole (unit)|mol]]', 20 => '|-', 21 => '| [[Melting point]]', 22 => '| {{convert|0.00|C|K|lk=on}}<ref name="VSMOW">[[Vienna Standard Mean Ocean Water]] (VSMOW), used for calibration, melts at 273.1500089(10)&nbsp;[[Kelvin|K]] (0.000089(10)&nbsp;°C) and boils at 373.1339&nbsp;K (99.9839&nbsp;°C)</ref>', 23 => '|-', 24 => '| [[Boiling point]]', 25 => '| {{convert|99.98|C|K}}<ref name="VSMOW" />', 26 => '|-', 27 => '| [[Specific gas constant]]', 28 => '| 461.5&nbsp;[[Joule|J]]/([[Kilogram|kg]]·K)', 29 => '|-', 30 => '| [[Heat of vaporization]]', 31 => '| 2.27&nbsp;[[Megajoule|MJ]]/kg', 32 => '|-', 33 => '| [[Heat capacity]] {{small|at 300 K}}', 34 => '| 1.864&nbsp;[[Kilojoule|kJ]]/(kg·K)<ref>{{cite web |title=Water Vapor – Specific Heat |url=http://www.engineeringtoolbox.com/water-vapor-d_979.html |access-date=May 15, 2012}}</ref>', 35 => '|}', 36 => '', 37 => ''''Water vapor''', '''water vapour''' or '''aqueous vapor''' is the [[gas]]eous phase of [[Properties of water|water]]. It is one [[Phase (matter)|state]] of water within the [[hydrosphere]]. Water [[vapor]] can be produced from the [[evaporation]] or [[boiling]] of liquid water or from the [[Sublimation (phase transition)|sublimation]] of [[ice]]. Water vapor is transparent, like most constituents of the atmosphere.<ref>{{cite web|title=What is Water Vapor?|url=http://www.weatherquestions.com/What_is_water_vapor.htm|access-date=2012-08-28}}</ref> Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by [[condensation]]. It is less dense than most of the other constituents of [[air]] and triggers [[convection]] currents that can lead to clouds and fog.', 38 => '', 39 => 'Being a component of Earth's hydrosphere and hydrologic cycle, it is particularly abundant in [[Earth's atmosphere]], where it acts as a [[greenhouse gas]] and warming feedback, contributing more to total greenhouse effect than non-condensable gases such as [[carbon dioxide]] and [[methane]]. Use of water vapor, as [[steam]], has been important for cooking, and as a major component in energy production and transport systems since the [[Steam power during the Industrial Revolution|industrial revolution]].', 40 => '', 41 => 'Water vapor is a relatively common atmospheric constituent, present even in the [[solar atmosphere]] as well as every planet in the [[Solar System]] and many [[astronomical object]]s including [[natural satellite]]s, [[comet]]s and even large [[asteroid]]s. Likewise the detection of [[Extrasolar object|extrasolar]] water vapor would indicate a similar distribution in other planetary systems. Water vapor can also be indirect evidence supporting the presence of extraterrestrial liquid water in the case of some planetary mass objects.', 42 => '', 43 => 'Water vapor, which reacts to temperature changes, is referred to as a 'feedback', because it amplifies the effect of forces that initially cause the warming. So, it is a greenhouse gas.<ref>{{Cite web |title=What is the greenhouse effect? |url=https://science.nasa.gov/climate-change/faq/what-is-the-greenhouse-effect/?fbclid=IwZXh0bgNhZW0CMTEAAR2K2LqG59TvqXSfzBFOQG4pyxRG7RnWKI0LBYujQWt5slI5Or-OhmaTEUQ_aem_AR_srupyQCizHFWfN8U8Mv7-6Q8w3jP1emq2iTAkXaomvxWN1O54HEb9bKAmHKZjriT0xU6q4eL6qLvBw1WiUwU3 |website=NASA}}</ref>', 44 => '', 45 => '== Properties ==', 46 => '', 47 => '=== Evaporation ===', 48 => 'Whenever a water molecule leaves a surface and diffuses into a surrounding gas, it is said to have [[Evaporation|evaporated]]. Each individual water molecule which transitions between a more associated (liquid) and a less associated (vapor/gas) state does so through the absorption or release of [[kinetic energy]]. The aggregate measurement of this kinetic energy transfer is defined as thermal energy and occurs only when there is differential in the temperature of the water molecules. Liquid water that becomes water vapor takes a parcel of heat with it, in a process called [[evaporative cooling]].<ref>{{harvp|Schroeder|2000|p=36}}</ref> The amount of water vapor in the air determines how frequently molecules will return to the surface. When a net evaporation occurs, the body of water will undergo a net cooling directly related to the loss of water.', 49 => '', 50 => 'In the US, the National Weather Service measures the actual rate of evaporation from a standardized "pan" open water surface outdoors, at various locations nationwide. Others do likewise around the world. The US data is collected and compiled into an annual evaporation map.<ref>{{cite web|url=http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId%3D208 |access-date=April 7, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080412215652/http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId=208 |archive-date=April 12, 2008 |title=Geotechnical, Rock and Water Resources Library - Grow Resource - Evaporation }}</ref> The measurements range from under 30 to over 120&nbsp;inches per year. Formulas can be used for calculating the rate of evaporation from a water surface such as a swimming pool.<ref>{{cite web|url=http://www.thermexcel.com/english/program/pool.htm|title=swimming, pool, calculation, evaporation, water, thermal, temperature, humidity, vapor, excel|access-date=February 26, 2016}}</ref><ref>{{cite web |url=http://www.rlmartin.com/rspec/whatis/equations.htm |archive-url=https://web.archive.org/web/20080324232701/http://www.rlmartin.com/rspec/whatis/equations.htm |archive-date=March 24, 2008 |title=Summary of Results of all Pool Evaporation Rate Studies |publisher=R. L. Martin & Associates}}</ref> In some countries, the evaporation rate far exceeds the [[Precipitation (meteorology)|precipitation]] rate.', 51 => '', 52 => 'Evaporative cooling is restricted by [[Standard temperature and pressure|atmospheric conditions]]. [[Humidity]] is the amount of water vapor in the air. The vapor content of air is measured with devices known as [[hygrometer]]s. The measurements are usually expressed as [[specific humidity]] or percent [[relative humidity]]. The temperatures of the atmosphere and the water surface determine the equilibrium vapor pressure; 100% relative humidity occurs when the partial pressure of water vapor is equal to the equilibrium vapor pressure. This condition is often referred to as complete saturation. Humidity ranges from 0&nbsp;grams per cubic metre in dry air to 30&nbsp;grams per cubic metre (0.03 ounce per cubic foot) when the vapor is saturated at 30&nbsp;°C.<ref>{{cite web|url=http://www.britannica.com/eb/article-53259/climate#292984.hook|title=climate - meteorology|website=Encyclopædia Britannica|access-date=February 26, 2016}}</ref>', 53 => '', 54 => '{{multiple image', 55 => ' |direction = horizontal', 56 => ' |align = right', 57 => ' |width1 = 165', 58 => ' |width2 = 176', 59 => ' |image1 = Meteorite Recovery Antarctica (retouched).jpg', 60 => ' |image2 = Tightjunction BBB.jpg', 61 => ' |caption1 = Recovery of [[meteorite]]s in Antarctica ([[ANSMET]])', 62 => ' |caption2 = [[Electron micrograph]] of freeze-etched [[capillary]] tissue', 63 => '}}', 64 => '', 65 => '=== Sublimation ===', 66 => '{{unreferenced-section|date=March 2024}}', 67 => '[[Sublimation (phase transition)|Sublimation]] is the process by which water molecules directly leave the surface of ice without first becoming liquid water. Sublimation accounts for the slow mid-winter disappearance of ice and snow at temperatures too low to cause melting. [[Antarctica]] shows this effect to a unique degree because it is by far the continent with the lowest rate of precipitation on Earth. As a result, there are large areas where [[Millennium|millennial]] layers of snow have sublimed, leaving behind whatever non-volatile materials they had contained. This is extremely valuable to certain scientific disciplines, a dramatic example being the collection of [[meteorite]]s that are left exposed in unparalleled numbers and excellent states of preservation.', 68 => '', 69 => 'Sublimation is important in the preparation of certain classes of biological specimens for [[Scanning electron microscope|scanning electron microscopy]]. Typically the specimens are prepared by [[cryofixation]] and [[Electron microscope|freeze-fracture]], after which the broken surface is freeze-etched, being eroded by exposure to vacuum until it shows the required level of detail. This technique can display protein molecules, [[organelle]] structures and [[lipid bilayer]]s with very low degrees of distortion.', 70 => '', 71 => '=== Condensation ===', 72 => '[[File:Above the Clouds.jpg|thumb|Clouds, formed by condensed water vapor]]', 73 => '', 74 => 'Water vapor will only condense onto another surface when that surface is cooler than the [[dew point]] temperature, or when the [[saturation vapor pressure|water vapor equilibrium]] in air has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface.<ref>{{Cite journal |last1=Held |first1=Isaac M. |last2=Soden |first2=Brian J. |title=Water vapor feedback and global warming |date=November 2000 |journal=Annual Review of Energy and the Environment|volume=25|issue=1|pages=441–475 |doi=10.1146/annurev.energy.25.1.441|issn=1056-3466}}</ref> The water molecule brings heat energy with it. In turn, the temperature of the atmosphere drops slightly.<ref>{{harvp|Schroeder|2000|p=19}}</ref> In the atmosphere, condensation produces clouds, fog and precipitation (usually only when facilitated by [[cloud condensation nuclei]]). The [[dew point]] of an air parcel is the temperature to which it must cool before water vapor in the air begins to condense. Condensation in the atmosphere forms cloud droplets.', 75 => '', 76 => 'Also, a net condensation of water vapor occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. [[Deposition (meteorology)|Deposition]] is a [[phase transition]] separate from condensation which leads to the direct formation of ice from water vapor. [[Frost]] and snow are examples of deposition.', 77 => '', 78 => 'There are several mechanisms of cooling by which condensation occurs:', 79 => '1) Direct loss of heat by conduction or radiation.', 80 => '2) Cooling from the drop in air pressure which occurs with uplift of air, also known as [[Adiabatic process|adiabatic cooling]].', 81 => 'Air can be lifted by mountains, which deflect the air upward, by convection, and by cold and warm fronts. ', 82 => '3) Advective cooling - cooling due to horizontal movement of air.', 83 => '', 84 => '=== Importance and Uses ===', 85 => '* Provides water for plants and animals: Water vapour gets converted to rain and snow that serve as a natural source of water for plants and animals.', 86 => '* Controls evaporation: Excess water vapor in the air decreases the rate of evaporation.', 87 => '* Determines climatic conditions: Excess water vapor in the air produces rain, fog, snow etc. Hence, it determines climatic conditions.', 88 => '', 89 => '=== Chemical reactions ===', 90 => 'A number of chemical reactions have water as a product. If the reactions take place at temperatures higher than the dew point of the surrounding air the water will be formed as vapor and increase the local humidity, if below the dew point local condensation will occur. Typical reactions that result in water formation are the burning of [[hydrogen]] or [[hydrocarbon]]s in air or other [[oxygen]] containing gas mixtures, or as a result of reactions with oxidizers.', 91 => '', 92 => 'In a similar fashion other chemical or physical reactions can take place in the presence of water vapor resulting in new chemicals forming such as [[rust]] on iron or steel, polymerization occurring (certain [[polyurethane]] foams and [[cyanoacrylate]] glues cure with exposure to atmospheric humidity) or forms changing such as where anhydrous chemicals may absorb enough vapor to form a crystalline structure or alter an existing one, sometimes resulting in characteristic color changes that can be used for [[humidity indicator card|measurement]].', 93 => '', 94 => '=== Measurement ===', 95 => 'Measuring the quantity of water vapor in a medium can be done directly or remotely with varying degrees of accuracy. Remote methods such [[Electromagnetic absorption by water|electromagnetic absorption]] are possible from satellites above planetary atmospheres. Direct methods may use electronic transducers, moistened thermometers or hygroscopic materials measuring changes in physical properties or dimensions.', 96 => '', 97 => '{| class="wikitable sortable" style="text-align: center; font-size: 85%; width: auto; table-layout: fixed;"', 98 => '|-', 99 => '! style="width:12em" |', 100 => '! medium', 101 => '! temperature range (degC)', 102 => '! measurement [[Measurement uncertainty|uncertainty]]', 103 => '! typical measurement frequency', 104 => '! system cost', 105 => '! notes', 106 => '|-', 107 => '! style="text-align:left;"| [[Hygrometer#Sling psychrometer|Sling psychrometer]]', 108 => '| air', 109 => '| −10 to 50', 110 => '| low to moderate', 111 => '| hourly', 112 => '| low', 113 => '|', 114 => '|-', 115 => '! style="text-align:left;"| Satellite-based spectroscopy', 116 => '| air', 117 => '| −80 to 60', 118 => '| low', 119 => '|', 120 => '| very high', 121 => '|', 122 => '|-', 123 => '! style="text-align:left;"| [[Hygrometer#Capacitive|Capacitive]] sensor', 124 => '| air/gases', 125 => '| −40 to 50', 126 => '| moderate', 127 => '| 2 to 0.05&nbsp;Hz', 128 => '| medium', 129 => '| prone to becoming saturated/contaminated over time', 130 => '|-', 131 => '! style="text-align:left;"| Warmed capacitive sensor', 132 => '| air/gases', 133 => '| −15 to 50', 134 => '| moderate to low', 135 => '| 2 to 0.05&nbsp;Hz (temp dependant)', 136 => '| medium to high', 137 => '| prone to becoming saturated/contaminated over time', 138 => '|-', 139 => '! style="text-align:left;"| [[hygrometer#Resistive|Resistive]] sensor', 140 => '| air/gases', 141 => '| −10 to 50', 142 => '| moderate', 143 => '| 60 seconds', 144 => '| medium', 145 => '| prone to contamination', 146 => '|-', 147 => '! style="text-align:left;"| Lithium chloride [[dewcell]]', 148 => '| air', 149 => '| −30 to 50', 150 => '| moderate', 151 => '| continuous', 152 => '| medium', 153 => '| see [[dewcell]]', 154 => '|-', 155 => '! style="text-align:left;"| [[Cobalt(II) chloride]]', 156 => '| air/gases', 157 => '| 0 to 50', 158 => '| high', 159 => '| 5 minutes', 160 => '| very low', 161 => '| often used in [[Humidity indicator card]]', 162 => '|-', 163 => '! style="text-align:left;"| [[Absorption spectroscopy]]', 164 => '| air/gases', 165 => '|', 166 => '| moderate', 167 => '|', 168 => '| high', 169 => '|', 170 => '|-', 171 => '! style="text-align:left;"| Aluminum oxide', 172 => '| air/gases', 173 => '|', 174 => '| moderate', 175 => '|', 176 => '| medium', 177 => '| see [[Moisture analysis]]', 178 => '|-', 179 => '! style="text-align:left;"| Silicon oxide', 180 => '| air/gases', 181 => '|', 182 => '| moderate', 183 => '|', 184 => '| medium', 185 => '| see [[Moisture analysis]]', 186 => '|-', 187 => '! style="text-align:left;"| Piezoelectric sorption', 188 => '| air/gases', 189 => '|', 190 => '| moderate', 191 => '|', 192 => '| medium', 193 => '| see [[Moisture analysis]]', 194 => '|-', 195 => '! style="text-align:left;"| Electrolytic', 196 => '| air/gases', 197 => '|', 198 => '| moderate', 199 => '|', 200 => '| medium', 201 => '| see [[Moisture analysis]]', 202 => '|-', 203 => '! style="text-align:left;"| [[Hygrometer#Hair tension hygrometers|Hair tension]]', 204 => '| air', 205 => '| 0 to 40', 206 => '| high', 207 => '| continuous', 208 => '| low to medium', 209 => '| Affected by temperature. Adversely affected by prolonged high concentrations', 210 => '|-', 211 => '! style="text-align:left;"| Nephelometer', 212 => '| air/other gases', 213 => '|', 214 => '| low', 215 => '|', 216 => '| very high', 217 => '|', 218 => '|-', 219 => '! style="text-align:left;"| [[Goldbeater's skin]] (Cow Peritoneum)', 220 => '| air', 221 => '| −20 to 30', 222 => '| moderate (with corrections)', 223 => '| slow, slower at lower temperatures', 224 => '| low', 225 => '| ref:WMO Guide to Meteorological Instruments and Methods of Observation No. 8 2006, (pages 1.12–1)', 226 => '|-', 227 => '! style="text-align:left;"| Lyman-alpha', 228 => '|', 229 => '|', 230 => '|', 231 => '| high frequency', 232 => '| high', 233 => '| http://amsglossary.allenpress.com/glossary/search?id=lyman-alpha-hygrometer1 Requires frequent calibration', 234 => '|-', 235 => '! style="text-align:left;"| [[hygrometer#Gravimetric|Gravimetric]] Hygrometer', 236 => '|', 237 => '|', 238 => '| very low', 239 => '|', 240 => '| very high', 241 => '| often called primary source, national independent standards developed in US, UK, EU & Japan', 242 => '|- class="sortbottom"', 243 => '!', 244 => '! medium', 245 => '! temperature range (degC)', 246 => '! measurement [[Measurement uncertainty|uncertainty]]', 247 => '! typical measurement frequency', 248 => '! system cost', 249 => '! notes', 250 => '|}', 251 => '', 252 => '=== Impact on air density ===', 253 => 'Water vapor is lighter or less [[Density of air|dense than dry air]].<ref>{{cite news| url=https://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/08/05/why-dry-air-is-heavier-than-humid-air/| title=Why dry air is heavier than humid air| newspaper=The Washington Post| date=August 5, 2013| access-date=28 December 2014| author=Williams, Jack}}</ref><ref>{{cite web| url=http://www.wwrf.org/humidity101.htm| archive-url=https://archive.today/20130416080406/http://www.wwrf.org/humidity101.htm| url-status=dead| archive-date=16 April 2013| title=Humidity 101| publisher=World Water rescue Foundation| access-date=28 December 2014}}</ref> At equivalent temperatures it is buoyant with respect to dry air, whereby the density of dry air at [[standard temperature and pressure]] (273.15 K, 101.325 kPa) is 1.27&nbsp;g/L and water vapor at standard temperature has a [[vapor pressure]] of 0.6 kPa and the much lower density of 0.0048&nbsp;g/L.', 254 => '', 255 => '==== Calculations ====', 256 => '[[File:dewpoint.jpg|right|frameless|upright=1.15]]', 257 => '', 258 => 'Water vapor and dry air density calculations at 0&nbsp;°C:', 259 => '* The [[molar mass]] of water is {{nowrap|18.02 g/mol}}, as calculated from the sum of the [[atomic mass]]es of its constituent [[atoms]].', 260 => '* The average molar mass of air (approx. 78% nitrogen, N₂; 21% oxygen, O₂; 1% other gases) is {{nowrap|28.57 g/mol}} at standard temperature and pressure ([[Standard temperature and pressure|STP]]).', 261 => '* Obeying [[Avogadro's Law]] and the [[ideal gas law]], [[Humidity|moist air]] will have a lower density than dry air. At max. saturation (i. e. rel. humidity = 100% at 0&nbsp;°C) the density will go down to 28.51 g/mol.', 262 => '* STP conditions imply a temperature of 0&nbsp;°C, at which the ability of water to become vapor is very restricted. Its [[concentration]] in air is very low at 0&nbsp;°C. The red line on the chart to the right is the maximum concentration of water vapor expected for a given temperature. The water vapor concentration increases significantly as the temperature rises, approaching 100% ([[steam]], pure water vapor) at 100&nbsp;°C. However the difference in densities between air and water vapor would still exist (0.598 vs. 1.27 g/L).', 263 => '', 264 => '==== At equal temperatures ====', 265 => 'At the same temperature, a column of dry air will be denser or heavier than a column of air containing any water vapor, the molar mass of diatomic [[nitrogen]] and diatomic [[oxygen]] both being greater than the molar mass of water. Thus, any volume of dry air will sink if placed in a larger volume of moist air. Also, a volume of moist air will rise or be [[Buoyancy|buoyant]] if placed in a larger region of dry air. As the temperature rises the proportion of water vapor in the air increases, and its buoyancy will increase. The increase in buoyancy can have a significant atmospheric impact, giving rise to powerful, moisture rich, upward air currents when the air temperature and sea temperature reaches 25&nbsp;°C or above. This phenomenon provides a significant driving force for [[Cyclone|cyclonic]] and [[Anticyclone|anticyclonic]] weather systems (typhoons and hurricanes).', 266 => '', 267 => '=== Respiration and breathing ===', 268 => 'Water vapor is a by-product of [[respiration (physiology)|respiration]] in plants and animals. Its contribution to the pressure, increases as its concentration increases. Its [[partial pressure]] contribution to air pressure increases, lowering the partial pressure contribution of the other atmospheric gases [[partial pressure|(Dalton's Law)]]. The total air pressure must remain constant. The presence of water vapor in the air naturally dilutes or displaces the other air components as its concentration increases.', 269 => '', 270 => 'This can have an effect on respiration. In very warm air (35&nbsp;°C) the proportion of water vapor is large enough to give rise to the stuffiness that can be experienced in humid jungle conditions or in poorly ventilated buildings.', 271 => '', 272 => '=== Lifting gas ===', 273 => 'Water vapor has lower density than that of [[air]] and is therefore [[buoyant]] in air but has lower vapor pressure than that of air. When water vapor is used as a [[lifting gas]] by a [[thermal airship]] the water vapor is heated to form steam so that its vapor pressure is greater than the surrounding air pressure in order to maintain the shape of a theoretical "steam balloon", which yields approximately 60% the lift of helium and twice that of hot air.<ref>{{cite web |last=Goodey |first=Thomas J. |title=Steam Balloons and Steam Airships |url=http://www.flyingkettle.com/jbfa.htm |access-date=August 26, 2010 |archive-date=August 30, 2010 |archive-url=https://web.archive.org/web/20100830180350/http://www.flyingkettle.com/jbfa.htm |url-status=dead }}</ref>', 274 => '', 275 => '=== General discussion ===', 276 => 'The amount of water vapor in an atmosphere is constrained by the restrictions of partial pressures and temperature. Dew point temperature and relative humidity act as guidelines for the process of water vapor in the [[water cycle]]. Energy input, such as sunlight, can trigger more evaporation on an ocean surface or more sublimation on a chunk of ice on top of a mountain. The ''balance'' between condensation and evaporation gives the quantity called [[vapor pressure|vapor partial pressure]].', 277 => '', 278 => 'The maximum partial pressure (''saturation pressure'') of water vapor in air varies with temperature of the air and water vapor mixture. A variety of empirical formulas exist for this quantity; the most used reference formula is the [[Goff-Gratch equation]] for the SVP over liquid water below zero degrees Celsius:', 279 => '', 280 => ':<math>\begin{align}', 281 => '\log_{10} \left( p \right) =', 282 => '& -7.90298 \left( \frac{373.16}{T}-1 \right) + 5.02808 \log_{10} \frac{373.16}{T} \\', 283 => '& - 1.3816 \times 10^{-7} \left( 10^{11.344 \left( 1-\frac{T}{373.16} \right)} -1 \right) \\', 284 => '& + 8.1328 \times 10^{-3} \left( 10^{-3.49149 \left( \frac{373.16}{T}-1 \right)} -1 \right) \\', 285 => '& + \log_{10} \left( 1013.246 \right)', 286 => '\end{align}</math>', 287 => '', 288 => 'where {{mvar|T}}, temperature of the moist air, is given in units of [[kelvin]], and {{mvar|p}} is given in units of [[millibar]]s ([[hectopascal]]s).', 289 => '', 290 => 'The formula is valid from about −50 to 102&nbsp;°C; however there are a very limited number of measurements of the vapor pressure of water over supercooled liquid water. There are a number of other formulae which can be used.<ref>{{cite web|url=http://cires.colorado.edu/~voemel/vp.html|title=Water Vapor Pressure Formulations|access-date=February 26, 2016}}</ref>', 291 => '', 292 => 'Under certain conditions, such as when the boiling temperature of water is reached, a net evaporation will always occur during standard atmospheric conditions regardless of the percent of relative humidity. This immediate process will dispel massive amounts of water vapor into a cooler atmosphere.', 293 => '', 294 => '[[Exhalation|Exhale]]d air is almost fully at equilibrium with water vapor at the body temperature. In the cold air the exhaled vapor quickly condenses, thus showing up as a fog or [[mist]] of water droplets and as condensation or frost on surfaces. Forcibly condensing these water droplets from exhaled breath is the basis of [[exhaled breath condensate]], an evolving medical diagnostic test.', 295 => '', 296 => 'Controlling water vapor in air is a key concern in the [[HVAC|heating, ventilating, and air-conditioning]] (HVAC) industry. [[Thermal comfort]] depends on the moist air conditions. Non-human comfort situations are called [[refrigeration]], and also are affected by water vapor. For example, many food stores, like supermarkets, utilize open chiller cabinets, or ''food cases'', which can significantly lower the water vapor pressure (lowering humidity). This practice delivers several benefits as well as problems.', 297 => '', 298 => '== {{anchor|Water vapor in Earth's atmosphere}} In Earth's atmosphere ==', 299 => '[[File:BAMS climate assess boulder water vapor 2002 - 2.png|thumb|upright=1.5|Evidence for increasing amounts of stratospheric water vapor over time in Boulder, Colorado.]]', 300 => '{{further|Atmosphere of Earth}}', 301 => '', 302 => 'Gaseous water represents a small but environmentally significant constituent of the [[Earth's atmosphere|atmosphere]]. The percentage of water vapor in surface air varies from 0.01% at -42&nbsp;°C (-44&nbsp;°F)<ref>{{harvp|McElroy|2002|loc=p. 34, Fig. 4.3a}}</ref> to 4.24% when the dew point is 30&nbsp;°C (86&nbsp;°F).<ref>{{harvp|McElroy|2002|loc=p. 36 example 4.1}}</ref> Over 99% of atmospheric water is in the form of vapour, rather than liquid water or ice,<ref>{{cite web|url=https://remss.com/measurements/atmospheric-water-vapor/|title=Atmospheric Water Vapor|work=Remote Sensing Systems|access-date=22 August 2021}}</ref> and approximately 99.13% of the water vapour is contained in the [[troposphere]]. The [[condensation]] of water vapor to the liquid or ice phase is responsible for [[clouds]], rain, snow, and other [[Precipitation (meteorology)|precipitation]], all of which count among the most significant elements of what we experience as weather. Less obviously, the [[latent heat of vaporization]], which is released to the atmosphere whenever condensation occurs, is one of the most important terms in the [[Earth's energy budget|atmospheric energy budget]] on both local and global scales. For example, latent heat release in atmospheric [[convection]] is directly responsible for powering destructive storms such as [[tropical cyclones]] and severe [[thunderstorms]]. Water vapor is an important [[greenhouse gas]]<ref name=Lacis /><ref name=ACS /> owing to the presence of the [[hydroxyl]] bond which strongly absorbs in the [[infra-red]].', 303 => '', 304 => 'Water vapor is the "working medium" of the atmospheric thermodynamic engine which transforms heat energy from sun irradiation into mechanical energy in the form of winds. Transforming thermal energy into mechanical energy requires an upper and a lower temperature level, as well as a working medium which shuttles forth and back between both. The upper temperature level is given by the soil or water surface of the Earth, which absorbs the incoming sun radiation and warms up, evaporating water. The moist and warm air at the ground is lighter than its surroundings and rises up to the upper limit of the troposphere. There the water molecules radiate their thermal energy into outer space, cooling down the surrounding air. The upper atmosphere constitutes the lower temperature level of the atmospheric thermodynamic engine. The water vapor in the now cold air condenses out and falls down to the ground in the form of rain or snow. The now heavier cold and dry air sinks down to ground as well; the atmospheric thermodynamic engine thus establishes a vertical convection, which transports heat from the ground into the upper atmosphere, where the water molecules can radiate it to outer space. Due to the Earth's rotation and the resulting Coriolis forces, this vertical atmospheric convection is also converted into a horizontal convection, in the form of cyclones and anticyclones, which transport the water evaporated over the oceans into the interior of the continents, enabling vegetation to grow.<ref>https://web.stanford.edu/~ajlucas/The%20Atmosphere%20as%20a%20Heat%20Engine.pdf {{Dead link|date=February 2022}}</ref>', 305 => '', 306 => 'Water in Earth's atmosphere is not merely below its boiling point (100&nbsp;°C), but [[Tropopause|at altitude]] it [[Lapse rate|goes below]] its freezing point (0&nbsp;°C), due to water's [[Hydrogen bond|highly polar attraction]]. When combined with its quantity, water vapor then has a relevant [[dew point]] and [[Dew point#Frost point|frost point]], unlike e. g., carbon dioxide and methane. Water vapor thus has a [[scale height]] a fraction of that of the bulk atmosphere,<ref>{{cite web |last=Gary |first=Bruce L. |url= http://brucegary.net/MTP_tutorial/MTP_ch5.html |title=Chapter 5:Atmospheric emission sources |work=Tutorial on airborne microwave temperature profilers |access-date=February 26, 2016}}</ref><ref name="History, AIP">{{cite web |url=http://www.aip.org/history/climate/co2.htm |title=The Carbon Dioxide Greenhouse Effect |access-date=February 26, 2016|url-status=dead |archive-date=November 11, 2016 |archive-url=https://web.archive.org/web/20161111201545/https://www.aip.org/history/climate/co2.htm}}</ref><ref>{{harvp|Weaver|Ramanathan|1995}}</ref> as the water [[Cloud|condenses]] and [[Precipitation|exits]], primarily in the [[troposphere]], the lowest layer of the atmosphere.<ref>{{cite journal|last=Norris |first=G.|title=Icy Surprise|journal=Aviation Week & Space Technology|volume=175 |issue=41 |page=30|date=2 Dec 2013|quote=22,000 ft., which is considered the upper limit for clouds containing supercooled liquid water}}</ref> Carbon dioxide ({{CO2|link=y}}) and [[methane]], being well-mixed in the atmosphere, tend to rise above water vapour. The absorption and emission of both compounds contribute to Earth's emission to space, and thus the [[Earth's energy budget|planetary greenhouse effect]].<ref name="History, AIP"/><ref>{{cite web|title=Climate scientists confirm elusive tropospheric hot spot|url=https://www.climatescience.org.au/content/873-climate-scientists-confirm-elusive-tropospheric-hot-spot|website=ARC Centre of Excellence for Climate System Science|date=May 14, 2015 |access-date=17 May 2015|archive-date=April 4, 2019|archive-url=https://web.archive.org/web/20190404154315/https://www.climatescience.org.au/content/873-climate-scientists-confirm-elusive-tropospheric-hot-spot|url-status=dead}}</ref><ref>{{cite journal|last1=Sherwood |first1=S|last2=Nishant |first2=N|title=Atmospheric changes through 2012 as shown by iteratively homogenized radiosonde temperature and wind data (IUKv2) |journal=Environmental Research Letters|date=11 May 2015|volume=10|issue=5|doi=10.1088/1748-9326/10/5/054007|page=054007|bibcode=2015ERL....10e4007S |doi-access=free}}</ref> This greenhouse forcing is directly observable, via distinct [[Spectroscopy|spectral features]] versus water vapor, and observed to be rising with rising {{CO2}} levels.<ref>{{cite journal |vauthors=Feldman DR, Collins WD, Gero PJ, Torn MS, Mlawer EJ, Shippert TR |title=Observational determination of surface radiative forcing by CO2 from 2000 to 2010|journal=Nature|date=25 February 2015 |volume=519|issue=7543 |doi=10.1038/nature14240|pages=339–343 |bibcode=2015Natur.519..339F|pmid=25731165 |s2cid=2137527|url=https://zenodo.org/record/1233331}}</ref> Conversely, adding water vapor at high altitudes has a disproportionate impact, which is why [[Environmental impact of aviation|jet traffic]]<ref>{{cite web |last1=Messer|first1=A|title=Jet contrails alter average daily temperature range |url=http://news.psu.edu/story/222587/2002/08/15/research/jet-contrails-alter-average-daily-temperature-range|access-date=17 May 2015}}</ref><ref>{{cite web|last1=Danahy|first1=A |title=Jets' contrails contribute to heat-trapping high-level clouds |url=http://news.psu.edu/story/265650/2013/02/21/research/jets%E2%80%99-contrails-contribute-heat-trapping-high-level-clouds|access-date=17 May 2015|archive-date=May 19, 2015|archive-url=https://web.archive.org/web/20150519073908/http://news.psu.edu/story/265650/2013/02/21/research/jets%E2%80%99-contrails-contribute-heat-trapping-high-level-clouds|url-status=dead}}</ref><ref>{{cite journal |last1=Ryan|first1=A |last2=Mackenzie|first2=A|title=World War II contrails: a case study of aviation-induced cloudiness|journal=International Journal of Climatology|date=September 2012|volume=32 |issue=11 |pages=1745–1753 |doi=10.1002/joc.2392 |bibcode=2012IJCli..32.1745R|s2cid=129296874 |display-authors=etal |doi-access=free}}</ref> has a disproportionately high warming effect. Oxidation of methane is also a major source of water vapour in the stratosphere,<ref>{{cite journal|last1=Noël|first1=Stefan|last2=Weigel |first2=Katja|display-authors=etal|date=2017 |title=Water Vapour and Methane Coupling in the Stratosphere observed with SCIAMACHY Solar Occultation Measurements |url=https://acp.copernicus.org/preprints/acp-2017-893/acp-2017-893.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://acp.copernicus.org/preprints/acp-2017-893/acp-2017-893.pdf |archive-date=2022-10-09 |url-status=live|journal=Atmospheric Chemistry and Physics|volume= |issue=18 |pages=4463–4476 |doi=10.5194/acp-18-4463-2018 |access-date=22 August 2021 |doi-access=free }}</ref> and adds about 15% to methane's global warming effect.<ref>{{cite journal |last1=Myhre |first1=Gunnar|display-authors=etal|date=9 January 2007 |title=Radiative forcing due to stratospheric water vapour from CH4 oxidation |journal= Geophysical Research Letters|volume=34 |issue=1 |doi=10.1029/2006GL027472 |bibcode=2007GeoRL..34.1807M|doi-access=free}}</ref>', 307 => '', 308 => 'In the absence of other greenhouse gases, Earth's water vapor would condense to the surface;<ref>{{harvp|Vogt|Butler|Rivera|Haghighipour|2010}}: "The equilibrium temperature of the Earth is 255&nbsp;K, well-below the freezing point of water, but because of its atmosphere, the [[greenhouse effect]] warms the surface"</ref><ref>{{cite web |url= http://www.astronomycafe.net/qadir/q1209.html |title=What is the maximum and minimum distance for the Earth that is compatible with life? |website=The Astronomy Cafe |url-status=deviated |archive-url=https://web.archive.org/web/20040510051659/http://www.astronomycafe.net/qadir/q1209.html |archive-date=2004-05-10}}</ref><ref>{{cite web |url=http://www.astronomynotes.com/solarsys/s3c.htm |title=Surface Temperature |website=Astronomy Notes |quote=for the Earth, the albedo is 0.306 and the distance is 1.000 AU, so the expected temperature is 254 K or -19 C – significantly below the freezing point of water!}}</ref> this [[Snowball Earth|has likely happened]], possibly more than once. Scientists thus distinguish between non-condensable (driving) and condensable (driven) greenhouse gases, i.e., the above water vapor feedback.<ref>de Pater, I., Lissauer, J., Planetary Sciences, Cambridge University Press, 2007</ref><ref name=ACS>{{cite web |url=http://www.acs.org/content/acs/en/climatescience/greenhousegases/properties.html |title=Properties |website=American Chemical Society|access-date=February 26, 2016}}</ref><ref name=Lacis>{{cite journal |vauthors=Lacis, A |display-authors=etal |title=The role of long-lived greenhouse gases as principal LW control knob that governs the global surface temperature for past and future climate change |journal=Tellus B |volume=65 |page=19734 |date=2013|doi=10.3402/tellusb.v65i0.19734 |bibcode=2013TellB..6519734L |s2cid=97927852 |doi-access=free }}</ref>', 309 => '', 310 => '[[Fog]] and clouds form through condensation around [[cloud condensation nuclei]]. In the absence of nuclei, condensation will only occur at much lower temperatures. Under persistent condensation or deposition, cloud droplets or snowflakes form, which [[precipitation (meteorology)|precipitate]] when they reach a critical mass.', 311 => '', 312 => 'Atmospheric concentration of water vapour is highly variable between locations and times, from 10&nbsp;ppmv in the coldest air to 5% (50 000 ppmv) in humid tropical air,<ref name="WallaceHobbs">{{cite book |last1=Wallace |first1=John M. |last2=Hobbs |first2=Peter V. |url=http://cup.aos.wisc.edu/453/2016/readings/Atmospheric_Science-Wallace_Hobbs.pdf |title=Atmospheric Science: An Introductory Survey |url-status=dead |archive-url=https://web.archive.org/web/20180728040037/http://cup.aos.wisc.edu/453/2016/readings/Atmospheric_Science-Wallace_Hobbs.pdf |archive-date=2018-07-28 |publisher=Elsevier |edition=2nd |year=2006 |isbn=978-0-12-732951-2 |page=8}}</ref> and can be measured with a combination of land observations, weather balloons and satellites.<ref>{{cite journal |last1=Li |first1=Zhenhong |last2=Muller |first2=Jan-Peter |last3=Cross |first3=Paul |date=29 October 2003 |title=Comparison of precipitable water vapor derived from radiosonde, GPS, and Moderate-Resolution Imaging Spectroradiometer measurements |journal= Journal of Geophysical Research: Atmospheres |volume=108 |issue=20 |page=4651 |doi=10.1029/2003JD003372 |bibcode=2003JGRD..108.4651L |doi-access=free }}</ref> The water content of the atmosphere as a whole is constantly depleted by precipitation. At the same time it is constantly replenished by evaporation, most prominently from oceans, lakes, rivers, and moist earth. Other sources of atmospheric water include combustion, respiration, volcanic eruptions, the transpiration of plants, and various other biological and geological processes. At any given time there is about 1.29 x 10¹⁶ litres (3.4 x 10¹⁵ gal.) of water in the atmosphere. The atmosphere holds 1 part in 2500 of the fresh water, and 1 part in 100,000 of the total water on Earth.<ref name="Gleick">{{cite book |last1=Gleick |first1=P. H. |editor1-last=Schneider |editor1-first=S. H. |title=Encyclopedia of Climate and Weather |date=1996 |publisher=Oxford University Press |location=New York |pages=817–823 |ref=Vol 2 |language=en |chapter=Water Resources |quote=Vol. 2}}</ref> The mean global content of water vapor in the atmosphere is roughly sufficient to cover the surface of the planet with a layer of liquid water about 25&nbsp;mm deep.<ref name=Forsythe>{{cite web |title=Observed Global and Regional Variation in Earth's Water Vapor: Focus on the Weather-Climate Interface|last1=Forsythe|first1=John |first2=Thomas H|last2=Haar|first3=Heather |last3=Cronk |url=https://gml.noaa.gov/publications/annual_meetings/2014/slides/22-140327-C.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://gml.noaa.gov/publications/annual_meetings/2014/slides/22-140327-C.pdf |archive-date=2022-10-09 |url-status=live|date=21 May 2014|access-date=22 August 2021}}</ref><ref>{{cite web|url=https://isccp.giss.nasa.gov/cgi-bin/fetch_graphs.cgi?BOI=333&REG=glb&PER=mon&ANALZ=anomdevs&SECTION=browseatmos|title=21-Year Deviations and Anomalies of Region Monthly Mean From Total Period Mean Over Global Total Column Water Vapor (cm)|author=International Satellite Cloud Climatology Project|date=2010|access-date=22 August 2021}}</ref><ref name=Mockler /> The mean annual precipitation for the planet is about 1 metre, a comparison which implies a rapid turnover of water in the air – on average, the residence time of a water molecule in the [[troposphere]] is about 9 to 10 days.<ref name=Mockler>{{cite journal |vauthors=Mockler SB |date=Dec 1995|title=Water vapor in the climate system |url=http://www.eso.org/gen-fac/pubs/astclim/espas/pwv/mockler.html |journal=AGU Special Report|access-date=22 August 2021}}</ref>', 313 => '', 314 => '[[File:20220726 Feedbacks affecting global warming and climate change - block diagram.svg |thumb|right |Some [[Effects of climate change|effects of global warming]] can either enhance ([[positive feedback]]s such as increased water vapor concentration) or inhibit ([[negative feedback]]s) warming.<ref>{{cite web |title=The Study of Earth as an Integrated System |date=2016 |url= https://climate.nasa.gov/nasa_science/science/ |website=nasa.gov |publisher=NASA |archive-url=https://web.archive.org/web/20161102022200/https://climate.nasa.gov/nasa_science/science/ |archive-date=2 November 2016 |url-status=live}}</ref><ref name=IPCC_AR6_SGI_FigTS.17>{{cite report |vauthors=Arias PA, Bellouin N, Coppola E, Jones RG, Krinner G, Marotzke J, Naik V, Palmer MD, ((Plattner G-K)), Rogelj J, Rojas M, Sillmann J, Storelvmo T, Thorne PW, Trewin R, Achuta Rao K, Adhikary B, Allan RP, Armour K, Bala G, Barimalala R, Berger S, Canadell JG, Cassou C, Cherchi A, Collins W, Collins WG, Connors SL, Corti S, Cruz F, Dentener FJ, Dereczynski C, Di Luca A, Diongue Niang A, Doblas-Reyes FJ, Dosio A, Douville H, Engelbrecht F, Eyring V, Fischer E, Forster P, Fox-Kemper B, Fuglestvedt JS, Fyfe JC, Gillett NP, Goldfarb L, Gorodetskaya I, Gutierrez JM, Hamdi R, Hawkins E, Hewitt HT, Hope P, Islam AS, Jones C, Kaufman DS, Kopp RE, Kosaka Y, Kossin J, Krakovska S, ((Lee J-Y)), Li J, Mauritsen T, Maycock TK, Meinshausen M, ((Min S-K)), ((Monteiro PMS)), Ngo-Duc T, Otto F, Pinto I, Pirani A, Raghavan K, Ranasinghe R, Ruane AC, Ruiz L, ((Sallée J-B)), Samset BH, Sathyendranath S, Seneviratne SI, Sörensson AA, Szopa S, Takayabu I, ((Tréguier A-M)), van den Hurk B, Vautard R, von Schuckmann K, Zaehle S, Zhang X, Zickfeld K |display-authors=0 |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |chapter=Technical Summary |veditors=Masson-Delmotte V, Zhai P, Pirani A, Connors SL, Péan C, Berger S, Caud N, Chen Y, Goldfarb L, Gomis MI, Huang M, Leitzell K, Lonnoy E, ((Matthews JBR)), Maycock TK, Waterfield T, Yelekçi O, Yu R, Zhou B |display-editors=0 |title=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=2021 |publisher=Cambridge University Press |place=Cambridge, United Kingdom and New York, NY, US |pages=33−144 [p. 96, Fig. TS.17] |doi=10.1017/9781009157896.002 |isbn=9781009157896 |archive-url=https://web.archive.org/web/20220721021347/https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |archive-date=21 July 2022|doi-access=free }}</ref>]]', 315 => 'Global mean water vapour is about 0.25% of the atmosphere by mass and also varies seasonally, in terms of contribution to atmospheric pressure between 2.62 hPa in July and 2.33 hPa in December.<ref>{{cite journal |last1=Trenberth |first1=Kevin E |last2=Smith |first2=Lesley |date=15 Mar 2005 |title=The Mass of the Atmosphere: A Constraint on Global Analyses |journal=Journal of Climate |volume=18 |issue=6 |pages=864–875 |doi=10.1175/JCLI-3299.1 |bibcode=2005JCli...18..864T |s2cid=16754900 |doi-access=free }}</ref> [[IPCC Sixth Assessment Report|IPCC AR6]] expresses medium confidence in increase of total water vapour at about 1-2% per decade;<ref>{{cite report', 316 => ' | vauthors = Gulev SK, Thorne PW, Ahn J, Dentener FJ, Domingues CM, Gerland S, Gong G, Kaufman DS, Nnamchi HC, Quaas J, Rivera JA, Sathyendranath S, Smith SL, Trewin B, von Shuckmann K, Vose RS', 317 => ' | date = 2021', 318 => ' | title = Changing State of the Climate System', 319 => ' | url = https://www.ipcc.ch/report/ar6/wg1/', 320 => ' | publisher = Cambridge University Press', 321 => ' | section = 2.3.1.3.3 Total column water vapour', 322 => ' | pages = 52–3', 323 => ' | work = Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change', 324 => ' | editor1-first = V', 325 => ' | editor1-last = Masson-Delmotte', 326 => ' | editor2-first = P ', 327 => ' | editor2-last = Zhai', 328 => ' | access-date = 22 August 2021', 329 => '}}', 330 => '</ref> it is expected to [[Clausius-Clapeyron relation|increase]] by around 7% per °C of warming.<ref name=Forsythe />', 331 => '', 332 => 'Episodes of surface geothermal activity, such as volcanic eruptions and geysers, release variable amounts of water vapor into the atmosphere. Such eruptions may be large in human terms, and major explosive eruptions may inject exceptionally large masses of water exceptionally high into the atmosphere, but as a percentage of total atmospheric water, the role of such processes is trivial. The relative concentrations of the various gases emitted by [[volcano]]es varies considerably according to the site and according to the particular event at any one site. However, water vapor is consistently the commonest [[volcanic gas]]; as a rule, it comprises more than 60% of total emissions during a [[subaerial eruption]].<ref>{{harvp|Sigurdsson|Houghton|2000}}</ref>', 333 => '', 334 => 'Atmospheric water vapor content is expressed using various measures. These include vapor pressure, [[specific humidity]], mixing ratio, dew point temperature, and [[relative humidity]].', 335 => '', 336 => '=== Radar and satellite imaging ===', 337 => '[[File:MYDAL2 M SKY WV.ogv|thumb|These maps show the average amount of water vapor in a column of atmosphere in a given month.(''click for more detail'')]]', 338 => '[[File:Atmospheric Water Vapor Mean.2005.030.jpg|thumb|[[MODIS]]/[[Terra (satellite)|Terra]] global mean atmospheric water vapor in atm-cm (centimeters of water in an atmospheric column if it condensed)]]', 339 => '', 340 => 'Because water molecules [[Absorption (electromagnetic radiation)|absorb]] [[microwave]]s and other [[radio wave]] frequencies, water in the atmosphere attenuates [[radar]] signals.<ref>{{harvp|Skolnik|1990|p=23.5}}</ref> In addition, atmospheric water will [[Reflection (physics)|reflect]] and [[refraction|refract]] signals to an extent that depends on whether it is vapor, liquid or solid.', 341 => '', 342 => 'Generally, radar signals lose strength progressively the farther they travel through the troposphere. Different frequencies attenuate at different rates, such that some components of air are opaque to some frequencies and transparent to others. Radio waves used for broadcasting and other communication experience the same effect.', 343 => '', 344 => 'Water vapor reflects radar to a lesser extent than do water's other two phases. In the form of drops and ice crystals, water acts as a prism, which it does not do as an individual [[molecule]]; however, the existence of water vapor in the atmosphere causes the atmosphere to act as a giant prism.<ref>{{harvp|Skolnik|1990|pp=2.44–2.54}}</ref>', 345 => '', 346 => 'A comparison of [[GOES-12]] satellite images shows the distribution of atmospheric water vapor relative to the oceans, clouds and continents of the Earth. Vapor surrounds the planet but is unevenly distributed. The image loop on the right shows monthly average of water vapor content with the units are given in centimeters, which is the [[precipitable water]] or equivalent amount of water that could be produced if all the water vapor in the column were to condense. The lowest amounts of water vapor (0 centimeters) appear in yellow, and the highest amounts (6 centimeters) appear in dark blue. Areas of missing data appear in shades of gray. The maps are based on data collected by the [[Moderate Resolution Imaging Spectroradiometer]] (MODIS) sensor on NASA's Aqua satellite. The most noticeable pattern in the time series is the influence of seasonal temperature changes and incoming sunlight on water vapor. In the tropics, a band of extremely humid air wobbles north and south of the equator as the seasons change. This band of humidity is part of the [[Intertropical Convergence Zone]], where the easterly trade winds from each hemisphere converge and produce near-daily thunderstorms and clouds. Farther from the equator, water vapor concentrations are high in the hemisphere experiencing summer and low in the one experiencing winter. Another pattern that shows up in the time series is that water vapor amounts over land areas decrease more in winter months than adjacent ocean areas do. This is largely because air temperatures over land drop more in the winter than temperatures over the ocean. Water vapor condenses more rapidly in colder air.<ref>{{cite web|url=http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYDAL2_M_SKY_WV|title=Water Vapor |publisher=Global Maps|access-date=February 26, 2016|date=2018-07-31 }}</ref>', 347 => '', 348 => 'As water vapor absorbs light in the visible spectral range, its absorption can be used in spectroscopic applications (such as [[Differential optical absorption spectroscopy|DOAS]]) to determine the amount of water vapor in the atmosphere. This is done operationally, e.g. from the Global [[Ozone]] Monitoring Experiment (GOME) spectrometers on [[European Remote-Sensing Satellite|ERS]] (GOME) and [[MetOp]] (GOME-2).<ref>{{cite web |last1=Loyola|first1=Diego|title=GOME-2/MetOp-A at DLR |website=atmos.eoc.dlr.de |url= http://atmos.eoc.dlr.de/gome/product_h2o.html |access-date=19 October 2017 |archive-date=October 17, 2017 |archive-url=https://web.archive.org/web/20171017095933/http://atmos.eoc.dlr.de/gome/product_h2o.html |url-status=dead}}</ref> The weaker water vapor absorption lines in the blue spectral range and further into the UV up to its dissociation limit around 243&nbsp;nm are mostly based on quantum mechanical calculations<ref name=TennysonFPrinciples>{{cite journal |last1=Tennyson|first1=Jonathan|title=Vibration–rotation transition dipoles from first principles|journal=Journal of Molecular Spectroscopy|date=2014 |volume=298|pages=1–6 |doi=10.1016/j.jms.2014.01.012|bibcode= 2014JMoSp.298....1T|doi-access=free}}</ref> and are only partly confirmed by experiments.<!--THE AUTHOR LIST AND TITLE DO NOT MATCH THE REST OF THE CITATION--<ref name=IUPACIII>{{cite journal|vauthors=Tennyson J, Bernath PF, Brown LR, Campargue A, Carleer MR, Csa´sza´r AG, Daumont L, Gamache RR, es, J. T. H., Naumenko OV, Polyansky OL, Rothmam LS, Vandaele AC, Zobov NF, Al Derzi AR, F´abri C, Fazliev AZ, rtenbacher TF, Gordon IE, Lodi L, Mizus II|title=IUPAC critical evaluation of the rotational-vibrational spectra of 1440 water vapor. Part III}}</ref>--><ref>{{cite journal |last1=Thalman |first1=Ryan |last2=Volkamer |first2=Rainer |title=Temperature dependent absorption cross-sections of O2-O2 collision pairs between 340 and 630 nm and at atmospherically relevant pressure |journal=Physical Chemistry Chemical Physics |date=2013|volume=15|issue=37|pages=15.371–381 |doi=10.1039/C3CP50968K |pmid=23928555 |bibcode=2013PCCP...1515371T}}</ref>', 349 => '', 350 => '=== Lightning generation ===', 351 => '{{see also|Van de Graaff generator}}', 352 => '', 353 => 'Water vapor plays a key role in [[lightning]] production in the atmosphere. From [[cloud physics]], usually clouds are the real generators of static [[electric charge|charge]] as found in Earth's atmosphere. The ability of clouds to hold massive amounts of electrical energy is directly related to the amount of water vapor present in the local system.', 354 => '', 355 => 'The amount of water vapor directly controls the [[permittivity]] of the air. During times of low humidity, static discharge is quick and easy. During times of higher humidity, fewer static discharges occur. Permittivity and capacitance work hand in hand to produce the megawatt outputs of lightning.<ref>{{harvp|Shadowitz|1975|pp=165–171}}</ref>', 356 => '', 357 => 'After a cloud, for instance, has started its way to becoming a lightning generator, atmospheric water vapor acts as a substance (or [[electrical insulation|insulator]]) that decreases the ability of the cloud to [[electrostatic discharge|discharge]] its electrical energy. Over a certain amount of time, if the cloud continues to generate and store more [[static electricity]], the barrier that was created by the atmospheric water vapor will ultimately break down from the stored electrical potential energy.<ref>{{harvp|Shadowitz|1975|pp=172–173, 182, 414–416}}</ref> This energy will be released to a local oppositely charged region, in the form of lightning. The strength of each discharge is directly related to the atmospheric permittivity, capacitance, and the source's charge generating ability.<ref>{{harvp|Shadowitz|1975|p=172}}</ref>', 358 => '', 359 => '== Extraterrestrial ==', 360 => '{{Further|Extraterrestrial liquid water}}', 361 => '', 362 => 'Water vapor is common in the [[Solar System]] and by extension, other [[planetary system]]s. Its signature has been detected in the atmospheres of the Sun, occurring in [[sunspots]]. The presence of water vapor has been detected in the atmospheres of all seven extraterrestrial planets in the Solar System, the Earth's Moon,<ref>{{harvp|Sridharan|Ahmed|Dasa|Sreelathaa|2010|p=947}}</ref> and the moons of other planets,{{which|date=June 2017}} although typically in only trace amounts.', 363 => '', 364 => '[[File:Artist's Concept of Europa Water Vapor Plume.jpg|thumb|left|upright|[[Cryogeyser]] erupting on Jupiter's moon [[Europa (moon)|Europa]] (artist concept)<ref name="NASA-20131212-EU" />]]', 365 => '', 366 => '[[File:Atmosphere of exoplanet.jpg|thumb|Artist's illustration of the signatures of water in exoplanet atmospheres detectable by instruments such as the [[Hubble Space Telescope]].<ref>{{cite news|title=Hubble traces faint signatures of water in exoplanet atmospheres (artist's illustration)|url=http://www.spacetelescope.org/images/opo1354a/|access-date=5 December 2013|newspaper=ESA/Hubble Press Release}}</ref>]]', 367 => '', 368 => 'Geological formations such as [[cryogeyser]]s are thought to exist on the surface of several [[icy moons]] ejecting water vapor due to [[tidal heating]] and may indicate the presence of substantial quantities of subsurface water. Plumes of water vapor have been detected on Jupiter's moon [[Europa (moon)|Europa]] and are similar to plumes of water vapor detected on Saturn's moon [[Enceladus]].<ref name="NASA-20131212-EU">{{cite web |last1=Cook |first1=Jia-Rui C.|last2=Gutro |first2=Rob |last3=Brown |first3=Dwayne |last4=Harrington |first4=J.D. |last5=Fohn |first5=Joe |title=Hubble Sees Evidence of Water Vapor at Jupiter Moon |url=http://www.jpl.nasa.gov/news/news.php?release=2013-363 |date=December 12, 2013 |website=[[NASA]] |access-date=December 12, 2013}}</ref> Traces of water vapor have also been detected in the stratosphere of [[Titan (moon)|Titan]].<ref>{{harvp|Cottini|Nixon|Jennings|Anderson|2012}}</ref> Water vapor has been found to be a major constituent of the atmosphere of [[dwarf planet]], [[Ceres (dwarf planet)|Ceres]], largest object in the [[asteroid belt]]<ref>{{harvp|Küppers|O'Rourke|Bockelée-Morvan|Zakharov|2014}}</ref> The detection was made by using the [[Far-infrared astronomy|far-infrared abilities]] of the [[Herschel Space Observatory]].<ref name="NASA-20140122">{{cite web |last1=Harrington |first1=J.D. |title=Herschel Telescope Detects Water on Dwarf Planet – Release 14-021 |url=http://www.nasa.gov/press/2014/january/herschel-telescope-detects-water-on-dwarf-planet |date=January 22, 2014 |website=[[NASA]] |access-date=January 22, 2014 }}</ref> The finding is unexpected because [[comets]], not [[asteroids]], are typically considered to "sprout jets and plumes." According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."<ref name="NASA-20140122" /> Scientists studying [[Mars]] hypothesize that if water moves about the planet, it does so as vapor.<ref>Jakosky, Bruce, et al. "Water on Mars", April 2004, ''Physics Today'', p. 71.</ref>', 369 => '', 370 => 'The brilliance of [[comet]] tails comes largely from water vapor. On approach to the [[Sun]], the ice many comets carry [[Sublimation (phase transition)|sublimes]] to vapor. Knowing a comet's distance from the sun, astronomers may deduce the comet's water content from its brilliance.<ref>{{cite web |website=rosetta.jpl.nasa.gov |url=http://rosetta.jpl.nasa.gov/science/comet-primer/anatomy-comet |archive-url=https://web.archive.org/web/20130218192113/http://rosetta.jpl.nasa.gov/science/comet-primer/anatomy-comet |archive-date=2013-02-18 |title=Anatomy of a Comet}}</ref>', 371 => '', 372 => 'Water vapor has also been confirmed outside the Solar System. Spectroscopic analysis of [[HD 209458 b]], an extrasolar planet in the constellation Pegasus, provides the first evidence of atmospheric water vapor beyond the Solar System. A star called [[IRC +10216|CW Leonis]] was found to have a ring of vast quantities of water vapor circling the aging, massive [[star]]. A [[NASA]] satellite designed to study chemicals in interstellar gas clouds, made the discovery with an onboard spectrometer. Most likely, "the water vapor was vaporized from the surfaces of orbiting comets."<ref>Lloyd, Robin. "Water Vapor, Possible Comets, Found Orbiting Star", 11 July 2001, [https://web.archive.org/web/20010713115441/http://www.space.com/searchforlife/swas_water_010711.html Space.com]. Retrieved December 15, 2006.</ref> Other exoplanets with evidence of water vapor include [[HAT-P-11b]] and [[K2-18b]].<ref name="NASA-20140924">{{cite web |last1=Clavin |first1=Whitney |last2=Chou |first2=Felicia |last3=Weaver |first3=Donna |last4=Villard |first4=Ray |last5=Johnson |first5=Michele |title=NASA Telescopes Find Clear Skies and Water Vapor on Exoplanet |url=http://www.jpl.nasa.gov/news/news.php?release=2014-322&1 |date=24 September 2014 |website=[[NASA]] |access-date=24 September 2014 }}</ref><ref>{{Cite journal | first1 = Angelos | last1 = Tsiaras | first2 = Ingo P. | last2 = Waldmann | first3 = Giovanna | last3 = Tinetti | first4 = Jonathan | last4 = Tennyson | first5 = Sergey N. | last5 = Yurchenko | display-authors = 1 | title = Water vapour in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b | journal = [[Nature Astronomy]] | volume = 3 | issue = 12 | pages = 1086–1091 | date = 11 September 2019 | doi = 10.1038/s41550-019-0878-9 | arxiv = 1909.05218 | bibcode = 2019NatAs...3.1086T | s2cid = 202558393 }}</ref>', 373 => '', 374 => '==See also==', 375 => '{{Div col|colwidth=15em}}', 376 => '* [[Air density]]', 377 => '* [[Atmospheric river]]', 378 => '* [[Boiling point]]', 379 => '* [[Condensation in aerosol dynamics]]', 380 => '* [[Deposition (meteorology)|Deposition]]', 381 => '* [[Earth's atmosphere]]', 382 => '* [[Eddy covariance]]', 383 => '* [[Equation of state]]', 384 => '* [[Evaporative cooler]]', 385 => '* [[Fog]]', 386 => '* [[Frost]]', 387 => '* [[Gas laws]]', 388 => '* [[Gibbs free energy]]', 389 => '* [[Gibbs phase rule]]', 390 => '* [[Greenhouse gas]]', 391 => '* [[Heat capacity]]', 392 => '* [[Heat of vaporization]]', 393 => '* [[Humidity]]', 394 => '* [[Hygrometer]]', 395 => '* [[Ideal gas]]', 396 => '* [[Kinetic theory of gases]]', 397 => '* [[Latent heat]]', 398 => '* [[Latent heat flux]]', 399 => '* [[Microwave radiometer]]', 400 => '* [[Phase of matter]]', 401 => '* [[Saturation vapor density]]', 402 => '* [[Steam]]', 403 => '* [[Sublimation (phase transition)|Sublimation]]', 404 => '* [[Superheating]]', 405 => '* [[Supersaturation]]', 406 => '* [[Thermodynamics]]', 407 => '* [[Troposphere]]', 408 => '* [[Vapor pressure]]', 409 => '{{Div col end}}', 410 => '', 411 => '== References ==', 412 => '{{Reflist|21em}}', 413 => '', 414 => '===Bibliography===', 415 => '{{refbegin|32em}}', 416 => '* {{cite journal |last1=Cottini |first1=V. |last2=Nixon |first2=C.&nbsp;A. |last3=Jennings |first3=D.&nbsp;E. |last4=Anderson |first4=C.&nbsp;M. |last5=Gorius |first5=N. |last6=Bjoraker |first6=G.L. |last7=Coustenis |first7=A. |last8=Teanby |first8=N.&nbsp;A. |last9=Achterberg |first9=R.&nbsp;K. |last10=Bézard |first10=B. |last11=de Kok |first11=R. |last12=Lellouch |first12=E. |last13=Irwin |first13=P.&nbsp;G.&nbsp;J. |last14=Flasar |first14=F.&nbsp;M. |last15=Bampasidis |first15=G. |year=2012 |title=Water vapor in Titan's stratosphere from Cassini CIRS far-infrared spectra |journal=[[Icarus (journal)|Icarus]] |volume=220 |issue=2 |pages=855–862 |doi=10.1016/j.icarus.2012.06.014 |bibcode=2012Icar..220..855C|hdl=2060/20140010836 |s2cid=46722419 |hdl-access=free }}', 417 => '* {{cite journal |last1=Küppers |first1=Michael |last2=O'Rourke |first2=Laurence |last3=Bockelée-Morvan |first3=Dominique|author3-link=Dominique Bockelée-Morvan |last4=Zakharov |first4=Vladimir |last5=Lee |first5=Seungwon |last6=von Allmen |first6=Paul |last7=Carry |first7=Benoît |last8=Teyssier |first8=David |last9=Marston |first9=Anthony |last10=Müller |first10=Thomas |last11=Crovisier |first11=Jacques |last12=Barucci |first12=M. 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Paul |last2=Butler |first3=E.&nbsp;J. |last3=Rivera |first4=N. |last4=Haghighipour |first5=Gregory W. |last5=Henry |first6=Michael H. |last6=Williamson |year=2010 |title=The Lick-Carnegie Exoplanet Survey: a 3.1 ''M''_⊕ planet in the habitable zone of the nearby M3V star Gliese 581 |journal=[[The Astrophysical Journal]] |volume=723 |issue=1 |pages=954–965 |doi=10.1088/0004-637X/723/1/954 |url=https://www.nsf.gov/news/newsmedia/goldilocks_planet/goldilocks_paper_gliese581.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.nsf.gov/news/newsmedia/goldilocks_planet/goldilocks_paper_gliese581.pdf |archive-date=2022-10-09 |url-status=live |format=PDF draft|arxiv = 1009.5733 |bibcode = 2010ApJ...723..954V |s2cid=3163906 }}', 426 => '* {{cite journal |last1=Weaver |first1=C.&nbsp;P. |last2=Ramanathan |first2=V. |year=1995 |title=Deductions from a simple climate model: factors governing surface temperature and atmospheric thermal structure |journal=[[Journal of Geophysical Research]] |volume=100 |issue=D6 |pages=11585–11591 |doi=10.1029/95jd00770 |url=http://www-ramanathan.ucsd.edu/files/pr63.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www-ramanathan.ucsd.edu/files/pr63.pdf |archive-date=2022-10-09 |url-status=live|bibcode = 1995JGR...10011585W }}', 427 => '{{refend}}', 428 => '', 429 => '==External links==', 430 => '{{commons}}', 431 => '* [https://web.archive.org/web/20021207072027/http://www.nsdl.arm.gov/Library/glossary.shtml National Science Digital Library – Water Vapor]', 432 => '* [http://www.sciencebits.com/exhalecondense Calculate the condensation of your exhaled breath]', 433 => '* [http://www.atmos.umd.edu/~stevenb/vapor/ Water Vapor Myths: A Brief Tutorial]', 434 => '* [http://www.eso.org/gen-fac/pubs/astclim/espas/pwv/mockler.html AGU Water Vapor in the Climate System – 1995]', 435 => '* [https://web.archive.org/web/20090218003456/http://phymetrix.com/Software.htm Free Windows Program, Water Vapor Pressure Units Conversion Calculator] – PhyMetrix', 436 => '', 437 => '{{Water}}', 438 => '{{Meteorological variables}}', 439 => '{{Authority control}}', 440 => '', 441 => '[[Category:Greenhouse gases]]', 442 => '[[Category:Atmospheric thermodynamics]]', 443 => '[[Category:Forms of water]]', 444 => '[[Category:Water in gas]]', 445 => '[[Category:Psychrometrics]]', 446 => '[[Category:Articles containing video clips]]' ]