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| − | A '''convection cell''' is a phenomenon of [[fluid dynamics]] which occurs in situations where there are [[temperature]] differences within a body of [[liquid]] or [[gas]].
| + | '''Orographic lift''' occurs when moisture-carrying [[cloud]]s floating over lower-[[elevation]] [[terrain]] move over rising terrain. As the clouds are forced to rise in [[altitude]] with the [[air]] which is carrying them, they cool. This cooler air cannot hold the moisture as well as warm air and this effectively raises the [[relative humidity]] to 100%, creating [[precipitation (meteorology)|precipitation]]. |
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| − | Fluids are materials which exhibit the property of [[flow]]. Both gasses and liquids have fluid properties, and even particulate solids such as flour, sand and gravel can behave as fluids. When a volume of fluid is heated, it expands and becomes less dense, and thus more buoyant than the surrounding fluid. The colder, more dense fluid settles underneath the warmer, less dense fluid and forces it to rise. Such a movement is called a [[convection]] current.
| + | Orographic Lift is demonstrated in many places in the world, but few examples are as clear as those in the [[United States]]. In the [[United States|U.S.]] states of [[Washington]] and [[Oregon]], places on the sea-facing side of the mountains see over 100 inches (over 2.5 m) of [[precipitation (meteorology)|precipitation]] per year. These places are on the side of the [[mountain]]s which is in the way of [[storm]] systems, and therefore receives the moisture which is effectively squeezed from the clouds. However, on the other side of the [[mountain]]s, sometimes as little as 15 miles (25 km) away, annual [[precipitation (meteorology)|precipitation]] can be as low as 8 inches (200 mm) per year. |
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| − | A rising body of fluid typically loses heat because it encounters a cold surface, because it exchanges heat with colder liquid through direct exchange, or in the example of the earth's [[atmosphere]], because it radiates heat. At some point the fluid becomes more dense than the fluid underneath it, which is still rising. Since it cannot descend through the rising fluid, it moves to one side. At some distance its downward force overcomes the rising force beneath it and the fluid begins to descend. As it descends, it warms again through surface contact, conductivity, or compression, and the cycle repeats itself. (The heating through compression of descending air is what is responsible for such welcome winter phenomena as what is known in Western North America as a [[chinook]] or in the Alps as a [[foehn]].)
| + | ==See also== |
| | + | *[[Orography]] |
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| − | A pattern of this type is called a '''convection cell'''. Convection cells can form in many kind of fluid situations, including the Earth's atmosphere, boiling water or soup (where the cells can be identified by particles they transport, such as rice), the ocean or the surface of the sun.
| + | [[Category:Climate forcing]] |
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| − | The size of a convection cell is largely determined by the fluid's properties, and they can even occur when the heating of a fluid is uniform.
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| − | <!--this picture is wrongwrongwrong, but leave it here for the code. I am tracking down copyright-free images to go here-->
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| − | <div style="float:right; margin-left:10px; margin-right:10px; width:300px; text-align:center"> [[image:convection cells and jupiter.jpg]]<br> <small>''Convection cells on the Sun <br>with Jupiter superimposed'' <br> </small> </div>
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| − | The [[Sun]]'s [[photosphere]] is composed of '''convection cells''' called granules, columns of superheated gas each approximately 1000 kilometres in diameter, hottest in the center (5800 degrees Celsius) with cooler gases falling in the narrow spaces between them.
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| − | ===External links===
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| − | * [http://www.solarviews.com/eng/edu/convect.htm Jet Propulsion Lab description of convection cells]
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| − | * [http://www.mountainnature.com/Climate/Chinook.htm Mountainnature.com - Chinook]
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Orographic lift occurs when moisture-carrying clouds floating over lower-elevation terrain move over rising terrain. As the clouds are forced to rise in altitude with the air which is carrying them, they cool. This cooler air cannot hold the moisture as well as warm air and this effectively raises the relative humidity to 100%, creating precipitation.
Orographic Lift is demonstrated in many places in the world, but few examples are as clear as those in the United States. In the U.S. states of Washington and Oregon, places on the sea-facing side of the mountains see over 100 inches (over 2.5 m) of precipitation per year. These places are on the side of the mountains which is in the way of storm systems, and therefore receives the moisture which is effectively squeezed from the clouds. However, on the other side of the mountains, sometimes as little as 15 miles (25 km) away, annual precipitation can be as low as 8 inches (200 mm) per year.
See also
