March 16, 2011
The photo above seemingly shows a sky calligraphed with clouds above Davos, Switzerland. In actuality, they're remnant contrails from Swiss Air Force F/A-18s jets made some hours before. These jets were engaged in training maneuvers. The spirals near the top of the picture result from a mock "dogfight" and are related to hole punch clouds and fall streaks. Note that the zenith is at the top of the photo and southwest is toward the bottom. The fact that these contrails remained intact since the training exercise ended indicates that both sufficient water vapor was present at the level of the jet maneuvers (perhaps 20,000 ft or 6,000 m) and that wind shear was minimal. Where the jets were guided in a steep trajectory, the contrails are more confined; longer sausage-like contrails appear where the jets followed a more horizontal flight path. Photo taken on February 14, 2011 at 4:30 p.m.