Everything about Orography totally explained
Orography is the average height of land, measured in
geopotential meters, over a certain domain. In
geoscientific models, such as
general circulation models, orography defines the lower boundary (except where there's ocean, of course). Because orography is spatially averaged, for example the height of the
Himalaya mountains will depend on horizontal
resolution. The higher the horizontal resolution, the better the orography will follow the actual terrain.
When a river's
tributaries or settlements by the river are listed in 'orographic sequence', they're in order from the highest (nearest the source of the river) to the lowest or
mainstem (nearest the mouth). This method of listing tributaries is the opposite of the
Strahler Stream Order, where the headwater tributaries are listed as category = 1.
Precipitation
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: 1) The upward deflection of large scale horizontal flow by the Orography. 2) The 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's being lifted will expand and cool. The expansion and cooling of a rising moist air parcel will allow for evaporation of the surrounding water vapor forming a
cloud and eventually 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 20 to 30 inches (500 to 750 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 (500 mm) per year at
Waikiki—and the tops of moderately high uplands are especially wet—about 475 in (12,000 mm) 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.
Further Information
Get more info on 'Orography'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://orography.totallyexplained.com">Orography Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
