Perlan Project - Meteorological Basis of The Project

Meteorological Basis of The Project

Standing Mountain waves are a source of rising air used in the sport of soaring. Riding these waves, similar in some ways to surfing on an ocean wave, has been widely used to reach great altitudes in sailplanes since they were discovered by German glider pilots, including Wolf Hirth, in 1933 in the Riesengebirge. This method uses the powerfully rising and sinking air in mountain waves. Gliders regularly climb in these waves to high altitudes. Currently, the glider absolute world altitude record stands at 15,460 meters (50,727 feet), which is the altitude reached by Steve Fossett and Einar Enevoldson. The previous record was 14,938 meters (49,009 feet). It was set in 1986 by Robert R. Harris, flying from California City and reaching his record height over Mount Whitney, California. This is thought to be near the limit for standing mountain waves in temperate latitudes, although in unusual meteorological conditions much higher altitudes may be achievable.

Standing waves normally do not extend above the tropopause at temperate latitudes. A strong west wind usually decreases above the tropopause, which has been shown to cap or prevent the upward propagation of standing mountain waves. However, at the outer boundary of the polar vortex, in winter, the stratospheric polar night jet exists. Its wind field can join with the wind field of the polar jet stream. The result is a wind which increases with altitude through the tropopause and upward to 100,000 feet or above. When this conjunction of winds occurs over a barrier mountain, standing mountain waves will propagate through that entire altitude range. Einar Enevoldson, former NASA test pilot and originator of The Perlan Project, sought to demonstrate the feasibility of riding these stratospheric standing mountain waves. The weather conditions favorable, although not in every case required to exist simultaneously for a climb into the stratospheric waves, are not exceptional:

• The stratospheric polar night jet overhead (occurring in near-polar latitudes during the late winter and early spring),
• Pre-frontal conditions,
• A gradual increase in wind speed with altitude,
• Wind direction within 30° of perpendicular to the mountain ridgeline,
• Strong low-altitude winds in a stable atmosphere,
• Ridge-top winds of at least 20 knots.

These conditions are likely to occur in the southern region of Patagonia three to four times per year between mid-August and mid-October. They probably occur in New Zealand, but less frequently; over the Antarctic Peninsula more frequently; and at several locations in the northern hemisphere, but closer to the North Pole at latitudes above 60° north.