Slope soaring
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Slope soaring is a gliding technique used to maintain altitude by flying in the updraft produced by wind blowing up the face of a steep slope. Model glider pilots commonly refer to this as "slope gliding" or "sloping". Pilots of full-sized gliders also call the lift "ridge lift" and its use "ridge flying". They use it to fly hundreds of kilometers where there is suitable terrain, such as in the Ridge-and-valley Appalachians. Birds, such as many seabirds (in particular albatross) and raptors, also use slopes in this way.
[edit] Basic requirements
Slope soaring requires a hill, ridge, escarpment or ocean wave, and a wind that is blowing against the slope, causing orographic lift. The wind creates a region of rising air directly above the slope which may extend some distance upwards and outwards from its face as the airflow follows the contour of the hill. However at near vertical cliffs, there is usually an area of turbulence with descending air near the base of the cliff. Downwind of the hill, lee waves can form that are also used by glider pilots to gain height but this should not be confused with slope lift.
The rising air from the slope is used to keep gliders airborne. Although a glider is always descending through the air, it will climb if the surrounding air is rising faster than the glider's sink rate.
