Airplane contrails oriented in various directions are seen here above the Cascade Range in Oregon. In this north-looking view, the snowcapped tops of South Sister, Mount Jefferson, and Mount Hood line up from south to north as white dots on the landscape. The white streaks behind airplanes form by a process similar to cloud formation. Specifically, contrails are formed as water vapor from aircraft engines condenses in cold, moist air. On a given day, in a location where conducive conditions exist, numerous intersecting and overlapping contrails can be observed, as in this scene. In heavily traveled air corridors, the net result of such artificial cloud formation may be locally significant. Researchers are just beginning to assess whether contrails might affect weather patterns — for example, by increasing the albedo (or reflectivity) of the atmosphere.
October–November 1993, image STS-58-85-77.