Iridescent aerodynamic contrails: The Norderney case of 27 June 2008

Abstract

An iridescent aerodynamic contrail (AerC) of a 2-engine aircraft flying from Amsterdam to Copenhagen was observed and photographed at Norderney on 27 June 2008, 14:06 UTC. In order to see whether this event was caused by an unusual weather situation we investigate the meteorological situation. It turns out that the situation allows AerC to become visible because it was warm enough and sufficiently moist. The dynamical situation is studied, and it seems that the stable stratification at the flight level of 350 hPa supports the appearance of an AerC. Additionally we investigate the ambient cloudiness where interesting halo features have been displayed in cirrus clouds. We examine the special colours of the Norderney aerodynamic contrail which allows to conclude that the width of the ice crystal size distribution is the factor directly relevant for iridescence, in this case representing a mixture from different growth histories. Finally we present an argumentation that AerC can be differentiated from jet contrails as soon as they display iridescence which requires an angular distance from the sun of less than about 30°.