region of high atmospheric pressure over the glacial ice fields of the interior of Greenland. This high-pressure area results from the cooling of the lower layers of the atmosphere because of the cold, underlying ice surface, such that the layers of air immediately over the ice fields are colder than the surrounding air at the same altitude over the neighbouring oceanic areas. This colder air, being more dense than the surrounding warmer air, produces the anticyclone. Because of the manner in which these anticyclones are formed, they tend to be shallow, surface phenomena, rarely extending to altitudes of 1,500 to 3,000 m (5,000 to 10,000 feet).