The polar vortex is the wintertime weather pattern in which the stratosphere flows counterclockwise around the North Pole. Scientists found that PSCs were almost always over very high latitude islands - an unexpected discovery. During the first flights of the DC-8 aircraft, scientists also found colder than expected temperatures inside the vortex northeast of Kiruna over Franz Josef Land, Russia. This proved to be an area of particularly good PSC hunting on later flights. The airborne researchers also measured the mountain waves that appear to contribute to PSC formation.
Mountain waves are waves in the atmosphere caused by wind flowing over mountain ranges.
The first balloon and its onboard instruments rose to more than 100,000 ft. Nov. 19, 1999. A second remote-sensing balloon flew to an altitude of 108,000 ft. Dec. 3, 1999. Both balloons landed safely in Finland.