Orography
Orographyis the study of thetopographic reliefofmountains,[1]and can more broadly include hills, and any part of a region's elevated terrain.[2]Orography (also known asoreography,orology,ororeology) falls within the broader discipline ofgeomorphology.[3]The term orography comes from theGreek:όρος,hill,γραφία,to write.
Uses[edit]
Mountain ranges and elevated land masses have a major impact on global climate. For instance, the elevated areas of East Africa substantially determine the strength of theIndian monsoon.[4]In scientific models, such asgeneral circulation models,orography defines the lower boundary of the model over land.[citation needed]
When a river'stributariesor 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 ormainstem(nearest the mouth).[citation needed]This method of listing tributaries is similar to theStrahler Stream Order,where the headwater tributaries are listed as category 1.
Orographic precipitation[edit]
 | It has been suggested that this section should besplitinto a new article titledOrographic precipitation.(discuss)(November 2020) |
Orographic precipitation, also known as relief precipitation, isprecipitationgenerated by a forced upward movement of air upon encountering a physiographic upland (seeanabatic wind). This lifting can be caused by:
- Upward deflection of large-scale horizontal flow by the orography.
- Anabatic or upward vertical propagation of moist air up an orographic slope, caused by daytime heating of the mountain barrier surface.
Upon ascent, the air that is being lifted expands and cools adiabatically. Thisadiabatic coolingof a rising moist air parcel may lower its temperature to itsdew point,thus allowing for condensation of the water vapor contained within it, and hence the formation of acloud.If enough water vapor condenses into cloud droplets, these droplets may become large enough to fall to the ground as precipitation.
Terrain-inducedprecipitation is a major factor formeteorologiststo consider when they forecast the local weather. Orography can play a major role in determining the type, amount, intensity, and duration of precipitation events. Researchers have discovered that barrier width, slope steepness, andupdraftspeed are major contributors when it comes to achieving the optimal amount and intensity of orographic precipitation.Computer modelssimulating these factors have shown that narrow barriers and steeper slopes produce stronger updraft speeds, which in turn increase orographic precipitation.
Orographic precipitation is known to occur on oceanicislands,such as theHawaiian IslandsandNew Zealand;much of the rainfall received on such islands is on the windward side, and theleewardside tends to be quite dry, almostdesert-like. This phenomenon results in substantial local gradients in the amount of average rainfall, with coastal areas receiving on the order of 20 to 30 inches (510 to 760 mm) per year, and interior uplands receiving over 100 inches (2,500 mm) per year. Leeward coastal areas are especially dry—less than 20 in (510 mm) per year atWaikiki—and the tops of moderately high uplands are especially wet—about 475 in (12,100 mm) per year atWai'ale'aleonKaua'i.
Another area in which orographic precipitation is known to occur is thePenninesin the north ofEngland:the west side of the Pennines receives more rain than the east because the clouds are forced up and over the hills and cause the rain to tend to fall on the western slopes. This is particularly noticeable betweenManchester(to the west) andLeeds(to the east); Leeds receives less rain due to a rain shadow of 12 miles (19 km) from the Pennines.
See also[edit]
References[edit]
- ^.Encyclopædia Britannica(11th ed.). 1911.
- ^OrographyArchived27 September 2007 at theWayback Machine(from theAmerican Meteorological Societywebsite)
- ^"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".World Digital Library.Retrieved23 January2013.
- ^Srinivasan, J., Nanjundiah, Ravi S. and Chakraborty, Arindam (2005)Impact of Orography on the Simulation of Monsoon Climate in a General Circulation ModelIndian Institute of Science
Sources[edit]
- Stull, Roland (2017).Practical Meteorology: An Algebra-based Survey of Atmospheric Science.University of British Columbia.ISBN978-0-88865-283-6.
- Whiteman, C. David (2000).Mountain Meteorology: Fundamentals and Applications.Oxford University Press.ISBN0-19-513271-8.
