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Atmospheric Humidity

 
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K.Haroon
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PostPosted: Tue Jun 07, 2011 7:49 pm    Post subject: Atmospheric Humidity Reply with quote

Atmospheric Humidity

The term humidity describes the fact that the atmosphere can contain water vapor. The amount of humidity found in air varies because of a number of factors. Two important factors are evaporation and condensation. At the water/atmosphere interface over our planet's oceans large amounts of liquid water are evaporated into atmospheric water vapor. This process is mainly caused by absorption of solar radiation and the subsequent generation of heat at the ocean's surface. In our atmosphere, water vapor is converted back into liquid form when air masses lose heat energy and cool. This process is responsible for the development of most clouds and also produces the rain that falls to the Earth's surface.

Scientists have developed a number of different measures of atmospheric humidity. We are primarily interested in three of these measures: mixing ratio, saturation mixing ratio, and relative humidity.

Mixing ratio is a measure that refers to the mass of a specific gas component relative to the mass of the remaining gaseous components for a sample of air. When used to measure humidity mixing ratio would measure the mass of water vapor relative to the mass of all of the other gases. In meteorological measurements, mixing ratio is usually expressed in grams of water vapor per kilogram of dry air.

Saturation mixing ratio refers to the mass of water vapor that can be held in a kilogram of dry air at saturation.

Saturation can be generally defined as the condition where any addition of water vapor to a mass of air leads to the condensation of liquid water or the deposition of ice at a given temperature and pressure.

Warmer air has a higher saturation mixing ratio than cooler air at a constant atmospheric pressure. It is important to note that this relationship between temperature and water vapor content in the air is not linear but exponential. In other words, for each 10 increase in temperature, saturation mixing ratio increases by a larger quantity.

The most commonly used measure of humidity is relative humidity.

Relative humidity can be simply defined as the amount of water in the air relative to the saturation amount the air can hold at a given temperature multiplied by 100. Air with a relative humidity of 50% contains a half of the water vapor it could hold at a particular temperature.

Read more with Illustrations at:
(http://www.physicalgeography.net/fundamentals/8c.html)


Last edited by K.Haroon on Sat Jun 25, 2011 9:07 am; edited 1 time in total
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K.Haroon
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PostPosted: Tue Jun 07, 2011 7:53 pm    Post subject: Exam Question Reply with quote

Exam Question Tips:

Arrow Relative humidity

A. Is higher in cool air than in warm air.

B. Increases if the air is cooled whilst maintaining the vapor pressure constant.

Answer: B

Warm air and cold air can be dry or moist; it is the change in temperature which results in a change in RH.

(http://www.atpforum.eu/showthread.php?p=42222)
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shprice



Joined: 24 Mar 2014
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Country: United Kingdom

PostPosted: Fri Apr 11, 2014 5:52 pm    Post subject: Relative Humidity Reply with quote

Arrow As Altitude Increases
Arrow Relative Humidity Increases

This can then be used to then calculate what happens with temperature changes; an increase in temperature would mean a decrease in altitude and therefore a decrease in relative humidity.
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