photo #8170633

What is this……......This ladies and gentlemen is a “Whole Aerodynamic Wake Condensation Trail”, also known as an “Iridescent Contrail”. They form due to cooling on an aircraft's wing, leading to condensation and ice formation in the planes wake. Unlike exhaust contrails, which are produced by the engines, these contrails are triggered by aerodynamic forces and can appear as beautiful, sometimes iridescent, trails behind the aircraft.For them to form, the plane must be flying heavy - at the beginning of a long haul flight when full of fuel. This causes large amounts of lift and extremely low pressure over the top of the wings. In humid conditions, this pressure reduction and temperature drop over a wing can cause water vapor to condense into tiny water droplets. If the air is supersaturated with respect to ice, these droplets freeze into ice particles, which then drift away from the wing and form a contrail. The colours are really seen because the angle between the plane, the observer and the sun must be quite small, around 10° or so for the colours to be visible.They usually form on sunny days at relatively high altitude around 30,000 feet or more. The iridescence observed is caused by individual water droplets diffracting sunlight, making a beautiful rainbow in the wake of the plane.