Orography

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An orographic map of Eastern Siberia from 1875 by Peter Kropotkin

Orography is the study of the

mountains,[1] and can more broadly include hills, and any part of a region's elevated terrain.[2] Orography (also known as oreography, orology, or oreology) falls within the broader discipline of geomorphology.[3] The term orography comes from the Greek
: όρος, hill, γραφία, to write.

Uses

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 the

Indian monsoon.[4] In scientific models, such as general circulation models, orography defines the lower boundary of the model over land.[citation needed
]

When a river's

Strahler Stream Order
, where the headwater tributaries are listed as category 1.

Orographic precipitation

Orographic precipitation occurs when moist air is forced upwards by terrain.

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:

  1. Upward deflection of large-scale horizontal flow by the orography.
  2. 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. 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.

Computer models
simulating 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 oceanic

Kaua'i
.

Another area in which orographic precipitation is known to occur is the Pennines in the north of England: 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 between Manchester (to the west) and Leeds (to the east); Leeds receives less rain due to a rain shadow of 12 miles (19 km) from the Pennines.

See also

References

  1. ^ "Orography" . Encyclopædia Britannica (11th ed.). 1911.
  2. ^ Orography Archived 27 September 2007 at the Wayback Machine (from the American Meteorological Society website)
  3. ^ "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. Retrieved 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

Sources

External links