| 词条 | Orography |
| 释义 |
UsesMountain ranges and elevated land masses have a major impact on global climate. For instance, the elevated areas of East Africa substantially determines the strength of the Indian monsoon.[4] In scientific models, such as general circulation models, orography defines the lower boundary of the model over land.{{Citation needed|date=January 2009}} When a river's tributaries or settlements by the river are listed in 'orographic sequence', they are in order from the highest (nearest the source of the river) to the lowest or mainstem (nearest the mouth).{{Citation needed|date=January 2009}} This method of listing tributaries is similar to the Strahler Stream Order, where the headwater tributaries are listed as category 1. Orographic precipitation{{refimprove section|date=January 2009}}{{see also|Orographic lift}}Orographic precipitation, also known as relief precipitation, is precipitation generated by a forced upward movement of air upon encountering a physiographic upland (see anabatic wind). This lifting can be caused by two mechanisms:
Upon ascent, the air that is being lifted will expand and cool. This adiabatic cooling of a rising moist air parcel may lower its temperature to its dew point, thus allowing for condensation of the water vapor contained within it, and hence the formation of a cloud. If enough water vapor condenses into cloud droplets, these droplets may become large enough to fall to the ground as precipitation. In parts of the world subjected to relatively consistent winds (for example the trade winds), a wetter climate prevails on the windward side of a mountain than on the leeward (downwind) side as moisture is removed by orographic precipitation. Drier air (see katabatic wind) is left on the descending, generally warming, leeward side where a rain shadow is formed. Terrain-induced precipitation is a major factor for meteorologists as they forecast the local weather. Orography can play a major role in the type, amount, intensity and duration of precipitation events. Researchers have discovered that barrier width, slope steepness and updraft speed are major contributors for the optimal amount and intensity of orographic precipitation. Computer model simulations for these factors showed that narrow barriers and steeper slopes produced stronger updraft speeds which, in turn, enhanced orographic precipitation. Orographic precipitation is well known on oceanic islands, such as the Hawaiian Islands or New Zealand, where much of the rainfall received on an island is on the windward side, and the leeward side tends to be quite dry, almost desert-like, by comparison. This phenomenon results in substantial local gradients of average rainfall, with coastal areas receiving on the order of {{convert|20|to|30|in|mm}} per year, and interior uplands receiving over {{convert|100|in|mm}} per year. Leeward coastal areas are especially dry—less than {{convert|20|in|mm|abbr=on}} per year at Waikiki—and the tops of moderately high uplands are especially wet—about {{convert|475|in|mm|abbr=on}} per year at Wai'ale'ale on Kaua'i. Another well known area for orographic precipitation is the Pennines in the north of England where the west side of the Pennines receives more rain than the east because the clouds (generally arriving from the west) are forced up and over the hills and cause the rain to fall preferentially on the western slopes. This is particularly noticeable between Manchester (West) and Leeds (East) where Leeds receives less rain due to a rain shadow of 12 miles from the Pennines. See also
References1. ^{{Cite EB1911|wstitle=Orography|short=x}} 2. ^Orography (from the American Meteorological Society website) 3. ^{{cite web|title=Map of the Southern Half of Eastern Siberia and Parts of Mongolia, Manchuria, and Sakhalin: For a General Sketch of the Orography of Eastern Siberia|url=http://www.wdl.org/en/item/125/|publisher=World Digital Library|accessdate=23 January 2013}} 4. ^Srinivasan, J., Nanjundiah, Ravi S. and Chakraborty, Arindam (2005) Impact of Orography on the Simulation of Monsoon Climate in a General Circulation Model Indian Institute of Science External links
2 : Climate forcing agents|Geomorphology |
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