Crow instability (named after its discoverer) happens when wingtip vortices do not dissipate prior to meeting up with jet exhaust contrails
Copyright: Brocken Inaglory [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Unusually clear skies and cool temperatures combined this morning (Monday, November 18, 2019) to create one of the most unique examples to date of spiral contrails that originate from the so-called Crow instability.
Contrails are a common phenomenon that occurs when the water vapor that is the natural byproduct of jet fuel combustion exits the engine nozzles and meets up with the super-chilled air of the upper atmosphere. The vapor immediately freezes without first going through the liquid phase, creating a multitude of micro ice crystals that reflect sunlight and are often visible for many miles.
Under certain rare atmospheric conditions, the wingtip vertices that are the result of the pressure differential between the lower and the upper surfaces of an aircraft wing in flight extend backwards and capture the ice particles as they form behind the aircraft. These particles then follow the streamlines of the vortex, appearing as a spiral or a series of rings.
This phenomenon was on spectacular display over the western Negev desert and the Gaza strip as IDF aircraft were performing high altitude reconnaissance overflights of the territory. The unusual sight inspired curiousity and even fear, with many residents on both sides of the border taking pictures and posting them to social media sites.
For the full story in the Hebrew and some spectacular images, please click here.
