A phenomenon that originates with a layer of cold air forming near the ground on a night with clear skies and a low pressure gradient. If the ground is sloping, the air close to the ground is colder than air at the same level but at some horizontal distance. The result is downslope gravitational flow of the colder, denser air beneath the warmer, lighter air. This occurs on the largest scale as the outflowing winds from Greenland and Antarctica. Contrast with anabatic wind.