Shown above are examples of crow instability
in jet condensation trails
(contrails) as observed over Davos, Switzerland
. The origin of the contrails was an Etihad Airbus
A380 (as identified by Meteosuisse
-- the Swiss governmental meteorologic board). This aircraft had cruised by at approximately 40,000 ft (12,190 m), 6 to 8 minutes prior to my observation of its contrail. According to Meteosuisse, the winds at the altitude where the Airbus was flying were only about 30 knots -- very light for this altitude
. After I first noticed these curious rotors, vortices
and loops they persisted for several minutes before dissipating.
The often sinusoidal oscillations associated with crow instability (photo at right) seem to be caused by the aircraft's wing tips that initiate small-scale turbulence in the airstream within the contrails and also create minor differences between the contrail's density and the density of the air surrounding them. Photos taken on October 24, 2015.