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| {{about|the meteorological dew point|the petroleum term|Hydrocarbon dew point}}
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| The '''dew point''' is the [[temperature]] at which the [[water vapor]] in [[air]] at constant [[barometric pressure]] [[Condensation|condense]]s into liquid water at the same rate at which it evaporates. At temperatures below the dew point, water will leave the air. The condensed water is called [[dew]] when it forms on a solid surface.
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| The dew point is a water-to-air saturation temperature. The dew point is associated with relative [[humidity]]. A high [[relative humidity]] indicates that the dew point is closer to the current air temperature. Relative humidity of 100% indicates the dew point is equal to the current temperature and that the air is maximally saturated with water. When the moisture content remains constant and temperature increases, relative humidity decreases.<ref name=Horstmeyer>{{Cite web| last=Horstmeyer | first=Steve | title=Relative Humidity....Relative to What? The Dew Point Temperature...a better approach | publisher=Steve Horstmeyer, Meteorologist, WKRC TV, Cincinnati, Ohio, USA | date=2006-08-15 | url=http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html| accessdate=2009-08-20}}</ref> | | Thrill Rides Of Las Vegas: Roller Coasters<br><br>The distinction among the jewelry you get a second or even get and jewellery, the present typically not in their very own way. 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Like a hummingbird, it was really a beautiful, but mysterious sight to see. |
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| [[General aviation]] pilots use dew-point data to calculate the likelihood of [[carburetor icing]] and [[fog]], and to estimate the height of the [[cloud base]].
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| [[Image:dewpoint.jpg|300px|right|thumb|This graph shows the maximum percentage, by mass, of water vapor that air at sea-level across a range of temperatures can contain.]]
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| At a given temperature but ''independent'' of [[barometric pressure]], the dew point is a consequence of the [[Humidity#Absolute humidity|absolute humidity]], the mass of water per unit volume of air. If both the temperature and pressure rise, however, the dew point will increase and the relative humidity will decrease accordingly. Reducing the absolute humidity without changing other variables will bring the dew point back down to its initial value. In the same way, increasing the absolute humidity after a temperature drop brings the dew point back down to its initial level. If the temperature rises in conditions of constant pressure, then the dew point will remain constant but the relative humidity will drop.
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| For this reason, a constant relative humidity (%) with different temperatures implies that when it's hotter, a higher fraction of the air is water vapor than when it's cooler.
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| At a given barometric pressure but ''independent'' of temperature, the dew point indicates the [[mole fraction]] of water vapor in the air, or, put differently, determines the [[specific humidity]] of the air. If the pressure rises without changing this mole fraction, the dew point will rise accordingly; Reducing the mole fraction, i.e., making the air less humid, would bring the dew point back down to its initial value. In the same way, increasing the mole fraction after a pressure drop brings the relative humidity back up to its initial level.
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| Considering New York (33 ft elevation) and Denver (5,280 ft elevation),<ref name="denfacts">{{cite web|url = http://www.denvergov.org/AboutDenver/today_factsguide.asp|title = Denver Facts Guide – Today|publisher = The City and County of Denver|accessdate =March 19, 2007}}</ref> for example, this means that if the dew point and temperature in both cities are the same, then the mass of water vapor per cubic meter of air will be the same, but the mole fraction of water vapor in the air will be greater in Denver.
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| ==Relationship to human comfort==
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| When the air temperature is high, the body's ''[[thermoregulation]]'' uses evaporation of [[perspiration]] to cool down, with the cooling effect directly related to how fast the perspiration evaporates. The rate at which perspiration can evaporate depends on how much [[humidity|moisture]] is in the air and how much moisture the air can hold. If the air is already saturated with moisture, perspiration will not evaporate. The body's cooling system will produce perspiration in an effort to keep the body at its normal temperature even when the rate it is producing sweat exceeds the evaporation rate. So even without generating additional body heat by exercising, one can become coated with sweat on humid days. It is the unevaporated sweat that tends to make one feel uncomfortable in humid weather.
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| As the air surrounding one's body is warmed by body heat, it will rise and be replaced with other air. If air is moved away from one's body with a natural breeze or a fan, sweat will evaporate faster, making perspiration more effective at cooling the body. The more unevaporated perspiration, the greater the discomfort.
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| A [[wet bulb thermometer]] also uses [[evaporative cooling]], so it provides a good analog for use in evaluating comfort level.
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| Discomfort also exists when the dew point is low (below around {{convert|-30|°C|°F|abbr=on}}). The drier air can cause skin to crack and become irritated more easily. It will also dry out the respiratory paths. [[Occupational Safety and Health Administration|OSHA]] recommends indoor air be maintained at {{convert|20|to|24.5|C|F}} with a 20-60% relative humidity (a dew point of {{convert|-4.5|to|15.5|C|F}}).<ref>http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=24602</ref>
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| Lower dew points, less than {{convert|10|°C|°F|abbr=on}}, correlate with lower ambient temperatures and the body requires less cooling. A lower dew point can go along with a high temperature only at extremely low relative humidity (see graph below), allowing for relatively effective cooling.
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| Those accustomed to [[continental climate]]s often begin to feel uncomfortable when the dew point reaches between {{convert|15|and|20|C|F}}. Most inhabitants of these areas will consider dew points above {{convert|21|°C|°F|abbr=on}} oppressive.
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| {| class="wikitable" style="text-align:center;"
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| ! colspan="2"|Dew point
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| ! Human perception<ref name=Horstmeyer/>
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| ! Relative humidity at {{convert|32|°C|°F|abbr=on}}
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| |-
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| | Over 26 °C
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| | Over 80 °F
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| | Severely high. Even deadly for [[asthma]] related illnesses
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| | 65% and higher
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| |-
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| | 24–26 °C
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| | 75–80 °F
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| | Extremely uncomfortable, fairly oppressive
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| | 62%
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| |-
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| | 21–24 °C
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| | 70–74 °F
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| | Very humid, quite uncomfortable
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| | 52–60%
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| |-
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| | 18–21 °C
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| | 65–69 °F
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| | Somewhat uncomfortable for most people at upper edge
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| | 44–52%
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| |-
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| | 16–18 °C
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| | 60–64 °F
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| | OK for most, but all perceive the humidity at upper edge
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| | 37–46%
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| |-
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| | 13–16 °C
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| | 55–59 °F
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| | Comfortable
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| | 38–41%
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| |-
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| | 10–12 °C
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| | 50–54 °F
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| | Very comfortable
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| | 31–37%
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| |-
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| | Under 10 °C
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| | Under 50 °F
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| | A bit dry for some
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| | 30%
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| |}
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| ==Measurement==
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| Devices called dew point meters are used to measure dew point over a wide range of temperatures. These devices consist of a polished metal mirror which is cooled as air is passed over it. The temperature at which dew forms is, by definition, the dew point. Manual devices of this sort can be used to calibrate other types of humidity sensors, and automatic sensors may be used in a control loop with a humidifier or dehumidifier to control the dew point of the air in a building or in a smaller space for a manufacturing process.
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| ==Calculating the dew point==
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| {{See also|Psychrometric chart}}
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| [[Image:Dewpoint-RH.svg|thum |center|Graph of the dependence of the dew point upon air temperature for several levels of relative humidity.]]
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| A well-known approximation used to calculate the dew point, ''T<sub>dp</sub>'', given just the actual ("dry bulb") air temperature, ''T'' and [[relative humidity]] (in percent), ''RH'', is the ''Magnus formula'':
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| :::<math>\begin{align}
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| \gamma(T,R\!H)&=\ln\left(\frac{R\!H}{100}\exp\left(\frac{bT}{c+T}\right)\right)=\ln\left(\frac{R\!H}{100}\right)+\frac{bT}{c+T};\\
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| T_{dp}&= \frac{c\gamma(T,R\!H)}{b-\gamma(T,R\!H)};\end{align}
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| </math>
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| The more complete formulation and origin of this approximation involves the interrelated [[Saturation (chemistry)|saturated]] water vapor pressure (in units of [[bar (unit)|millibar]], which is also [[Pascal (unit)|hPa]]) at ''T'', ''P<sub>s</sub>''(''T''), and the actual water vapor pressure (also in units of millibar), ''P<sub>a</sub>''(''T''), which can be either found with ''RH'' or approximated with the barometric pressure (in millibar units), ''BP<sub>mb</sub>'', and "[[wet-bulb temperature|wet-bulb]]" temperature, ''T<sub>w</sub>'' is:
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| :::<small>Note: unless declared otherwise, all temperatures are expressed and worked in degrees Celsius</small>
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| ::::<math>
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| \begin{align}
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| P_s(T)& = \frac{100}{R\!H}P_\text{a}(T) = a\exp\left(\frac{bT}{c+T}\right);\\[8pt]
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| P_\text{a}(T) & = \frac{R\!H}{100}P_s(T)=a\exp(\gamma(T,R\!H)),\\
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| &\approx P_s(T_\text{w}) - B\!P_\text{mb} 0.00066 \left[1 + (0.00115T_\text{w} \right)]\left(T-T_\text{w}\right);\\[5pt]
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| T_\text{dp} & = \frac{c\ln(P_\text{a}(T)/a)}{b-\ln(P_\text{a}(T)/a)};\end{align}</math>
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| For greater accuracy, ''P<sub>s</sub>''(''T'') (and, therefore, γ(''T'',''RH'')) can be enhanced, using part of the ''Bögel modification'', also known as the [[Arden Buck equation]], which adds a fourth, ''d'' constant:
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| :::<math>\begin{align}P_{s:m}(T)&=a\exp\bigg(\left(b-\frac{T}{d}\right)\left(\frac{T}{c+T}\right)\bigg);\\[8pt]
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| \gamma_m(T,R\!H)&=\ln\Bigg(\frac{R\!H}{100}\exp
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| \bigg(\left(b-\frac{T}{d}\right)\left(\frac{T}{c+T}\right)\bigg)
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| \Bigg);\\
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| T_{dp}&= \frac{c\gamma_m(T,R\!H)}{b-\gamma_m(T,R\!H)};\end{align}</math>
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| :::''(where <math>\scriptstyle{a=6.1121\ \mathrm{millibar};\quad\;b= 18.678;\quad\;c= 257.14^\circ \mathrm{C};\quad\;d=234.5^\circ \mathrm{C}.}</math>)''
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| There are several different constant sets in use. The ones used in [[NOAA]]'s presentation <ref>http://www.srh.noaa.gov/images/epz/wxcalc/rhTdFromWetBulb.pdf ''Relative Humidity and Dewpoint Temperature from Temperature and Wet-Bulb Temperature''</ref> are taken from a 1980 paper by David Bolton in the ''Monthly Weather Review'':<ref>[https://www.rsmas.miami.edu/users/pzuidema/Bolton.pdf "''The computation of equivalent potential temperature''", Monthly Weather Review], vol.108, pg.1047, Eq.10</ref>
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| :<math>\begin{align}a&=6.112\ \mathrm{millibar};\quad\;b&= 17.67;\quad\;c&= 243.5^\circ \mathrm{C};\end{align}</math>
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| These valuations provide a minimum accuracy of 0.1%, for
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| :::::-30°C ≤ ''T'' ≤ +35°C;
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| ::::::1% < ''RH'' < 100%;
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| Also noteworthy is the Sonntag1990,<ref>[http://irtfweb.ifa.hawaii.edu/~tcs3/tcs3/Misc/Dewpoint_Calculation_Humidity_Sensor_E.pdf SHTxx Application Note Dew-point Calculation]</ref>
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| :<math>\scriptstyle{a=6.112\ \mathrm{millibar};\quad\;b= 17.62;\quad\;c= 243.12^\circ \mathrm{C}:\quad -45^\circ \mathrm{C}\le T\le +60^\circ \mathrm{C}\quad (<-0.35^\circ \mathrm{C})}</math>
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| Another common set of values originates from the 1974 ''Psychrometry and Psychrometric Charts'', as presented by '''''Paroscientific''''',<ref>[http://www.paroscientific.com/dewpoint.htm MET4 AND MET4A CALCULATION OF DEW POINT]</ref>
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| :<math>\scriptstyle{a=6.105\ \mathrm{millibar};\quad\;b= 17.27;\quad\;c= 237.7^\circ \mathrm{C}:\quad 0^\circ \mathrm{C}\le T\le +60^\circ \mathrm{C}\quad (\pm0.4^\circ \mathrm{C})}</math>
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| Also, in the ''Journal of Applied Meteorology and Climatology'',<ref>Buck, A. L. (1981), [http://www.public.iastate.edu/~bkh/teaching/505/arden_buck_sat.pdf "New equations for computing vapor pressure and enhancement factor"], J. Appl. Meteorol. 20: 1527–1532</ref> Arden Buck presents several different valuation sets, with different minimum accuracies for different temperature ranges. Two particular sets provide a range of -40°C → +50°C between the two, with even greater minimum accuracy than all of the other, above sets (maximum error at given |C°| extreme): | |
| :<math>\scriptstyle{a=6.1121\ \mathrm{millibar};\quad\;b= 17.368;\quad\;c= 238.88^\circ \mathrm{C}:\quad\quad\! 0^\circ \mathrm{C}\le T\le +50^\circ \mathrm{C}\;\;(\le0.05%)}</math>
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| :<math>\scriptstyle{a=6.1121\ \mathrm{millibar};\quad\;b= 17.966;\quad\;c= 247.15^\circ \mathrm{C}:\quad -40^\circ \mathrm{C}\le T\le 0^\circ \mathrm{C}\quad\! \;\;(\le0.06%)}</math>
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| ===Simple approximation===
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| There is also a very simple approximation that allows conversion between the dew point, temperature and relative humidity. This approach is accurate to within about ±1°C as long as the relative humidity is above 50%:
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| :<math>T_{dp}\approx T-\frac{100-R\!H}{5};</math>
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| and
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| :<math>R\!H\approx 100-5(T-T_{dp});\,</math>
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| This can be expressed as a simple rule of thumb:
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| <blockquote>
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| ''For every 1°C difference in the dew point and dry bulb temperatures, the relative humidity decreases by 5%, starting with RH = 100% when the dew point equals the dry bulb temperature.''
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| </blockquote>
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| The derivation of this approach, a discussion of its accuracy, comparisons to other approximations, and more information on the history and applications of the dew point are given in the Bulletin of the American Meteorological Society.<ref>M. G. Lawrence, "The relationship between relative humidity and the dew point temperature in moist air: A simple conversion and applications", Bull. Am. Meteorol. Soc., 86, 225–233, 2005</ref>
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| For temperatures in degrees Fahrenheit, these approximations work out to
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| :<math> T_{dp:f}\approx T_{f}-\frac{9}{25}(100-R\!H);</math>
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| and
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| :<math> R\!H\approx 100-\frac{25}{9}(T_{f}-T_{dp:f});</math>
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| For example, a relative humidity of 100% means dew point is the same as air temp. For 90% RH, dew point is 3 degrees Fahrenheit lower than air temp. For every 10 percent lower, dew point drops 3 °F.
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| == Frost point ==
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| The '''frost point''' is similar to the dew point, in that it is the temperature to which a given parcel of humid air must be cooled, at constant barometric pressure, for water vapor to be [[Deposition (phase transition)|deposited]] on a surface as ice without going through the liquid phase. (Compare with [[Sublimation (phase transition)|sublimation]].) The frost point for a given parcel of air is always higher than the dew point, as the stronger bonding between water molecules on the surface of ice requires higher temperature to break.<ref>{{cite web | url=http://www.theweatherprediction.com/habyhints/347/ | title=Frost point and dew point | accessdate=September 30, 2011 | author=Haby, Jeff}}</ref>
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| == See also ==
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| * [[Bubble point]]
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| * [[Carburetor heat]]
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| * [[Hydrocarbon dew point]]
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| * [[Psychrometrics]]
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| * [[Thermodynamic diagrams]]
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| ==References==
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| {{Reflist|}}
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| ==External links==
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| * [http://weather.gov/glossary/index.php?word=dew+point Dew point definition] NOAA Glossary
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| * [http://www.faqs.org/faqs/meteorology/temp-dewpoint/ Often Needed Answers about Temp, Humidity & Dew Point] from the sci.geo.meteorology
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| {{Meteorological variables}}
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| {{DEFAULTSORT:Dew Point}}
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| [[Category:Atmospheric thermodynamics]]
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| [[Category:Psychrometrics]]
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| [[Category:Threshold temperatures]]
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| [[sv:Luftfuktighet#Daggpunkt]]
| |
Thrill Rides Of Las Vegas: Roller Coasters
The distinction among the jewelry you get a second or even get and jewellery, the present typically not in their very own way. A lot of jewelers dismiss the value of correctly displaying your art and feel the work is sold. It is not constantly the circumstance. So what makes a excellent representation of the jewelry?
Select a observe with characteristics and design that will be most fitting to her way of life and tastes. For case in point, if her working day usually is composed of outside outings like hiking or doing sporting activities like swimming or diving, a water-resistant sports activities view with both a compass or stopwatch purpose is the perfect gift for her. If she is a job female who resides in a company planet, go for a formal leather view that will match her professional aura. A gold or silver bracelet watch meanwhile can be the ideal adornment to the advanced outfit that she wears to social gatherings.
As I was drifting together the area, and seeking all around, I unsuccessful to discover that a Barracuda about two or 3 toes extended was appropriate smack under me. I was literately no considerably less than three ft away from him.
Make something for the baby. Crochet las vegas bracelet or quilt a blanket, generate a piece of artwork to hang in the nursery, sew an outfit, or collect photos to make it a family tree. Any gift created with adore will always be appreciated.
What about the housing marketplace. Reports are coming out every day about millions of Us citizens upside down on their properties. This basically signifies they owe more than the house is really worth. If you can make the mortgage payment, what do you treatment? Sure, you may possibly be upside down now, but what about a few to five many years down the line? The housing market will recover and so will the benefit of your home. Don't permit a legendary paper loss affect you.
las vegas came out swinging early but was unable to keep up that depth. 51s catcher J.P. Arencibia went 2-for-four with a two-operate prolonged bomb in the fourth, and shortstop Angel Sanchez went two-for-4 with a double. Next-baseman Joe Inglett went 2-for-four and designated hitter Randy Ruiz scored his 81st RBI of the period. Pitching was also a difficulty for Vegas baby bracelet with beginning still left-handed pitcher Davis Romero going 5 innings with one attained operate off of a few hits and three strikeouts, and righty Sean Stidfole earning his very first decline as a 51.
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