Dewpoint: Difference between revisions

Latest revision as of 14:03, 20 February 2012

dewpoint[edit | edit source]

(Or dewpoint temperature.) The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur.

When this temperature is below 0°C, it is sometimes called the frost point. The dewpoint may alternatively be defined as the temperature at which the saturation vapor pressure of the parcel is equal to the actual vapor pressure of the contained water vapor. Isobaric heating or cooling of an air parcel does not alter the value of that parcel's dewpoint, as long as no vapor is added or removed. Therefore, the dewpoint is a conservative property of air with respect to such processes. However, the dewpoint is nonconservative with respect to vertical adiabatic motions of air in the atmosphere. The dewpoint of ascending moist air decreases at a rate only about one-fifth as great as the dry-adiabatic lapse rate. The dewpoint can be measured directly by several kinds of dewpoint hygrometers or it can be deduced indirectly from psychrometers or devices that measure the water vapor density or mixing ratio.
See dewpoint formula.

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-<div class="definition"><div class="short_definition">(<br/>''Or'' [[dewpoint temperature]].) The [[temperature]] to which a given [[air parcel]] must be  cooled at constant [[pressure]] and constant water vapor content in order for [[saturation]] to occur.</div><br/> <div class="paragraph">When this temperature is below 0&deg;C, it is sometimes called the [[frost point]]. The dewpoint may  alternatively be defined as the temperature at which the [[saturation vapor pressure]] of the parcel  is equal to the actual [[vapor pressure]] of the contained [[water vapor]]. Isobaric heating or cooling  of an air parcel does not alter the value of that parcel's dewpoint, as long as no vapor is added or  removed. Therefore, the dewpoint is a [[conservative property]] of air with respect to such processes.  However, the dewpoint is nonconservative with respect to vertical [[adiabatic]] motions of air in the  [[atmosphere]]. The dewpoint of ascending [[moist air]] decreases at a rate only about one-fifth as great  as the [[dry-adiabatic lapse rate]]. The dewpoint can be measured directly by several kinds of [[dewpoint  hygrometers]] or it can be deduced indirectly from [[psychrometers]] or devices that measure  the water vapor density or [[mixing ratio]]. <br/>''See'' [[dewpoint formula]].</div><br/> </div>
+<div class="definition"><div class="short_definition">(''Or'' [[dewpoint temperature]].) The [[temperature]] to which a given [[air parcel]] must be  cooled at constant [[pressure]] and constant water vapor content in order for [[saturation]] to occur.</div><br/> <div class="paragraph">When this temperature is below 0&#x000b0;C, it is sometimes called the [[frost point]]. The dewpoint may  alternatively be defined as the temperature at which the [[saturation vapor pressure]] of the parcel  is equal to the actual [[vapor pressure]] of the contained [[water vapor]]. Isobaric heating or cooling  of an air parcel does not alter the value of that parcel's dewpoint, as long as no vapor is added or  removed. Therefore, the dewpoint is a [[conservative property]] of air with respect to such processes.  However, the dewpoint is nonconservative with respect to vertical [[adiabatic]] motions of air in the  [[atmosphere]]. The dewpoint of ascending [[moist air]] decreases at a rate only about one-fifth as great  as the [[dry-adiabatic lapse rate]]. The dewpoint can be measured directly by several kinds of [[dewpoint  hygrometers]] or it can be deduced indirectly from [[psychrometers]] or devices that measure  the water vapor density or [[mixing ratio]]. <br/>''See'' [[dewpoint formula]].</div><br/> </div>
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