Quando un aereo passa attraverso una nuvola modifica la pressione e abbassa la temperatura dell’aria anche di 20-30°C. In questo modo, promuove la condensazione delle gocce d’acqua in cristalli di ghiaccio, fenomeno che dà luogo ai caratteristici fori.
A “Hole Punch” cloud is a non-technical name given to a cloud formed from an aircraft dissipation hole or trail. They are also called “Punch Hole” clouds. Rather than extending as a line, Hole Punch clouds appear as a circular or oval hole in a deck or thin layer of supercooled water clouds. They are not uncommon where jet flight paths intersect altocumulus layers. What is uncommon is when they form in a perfect circle that persists for a length of time to be widely observed.
On December 11, 2003 that’s exactly what happened along the central Gulf Coast. A remarkably circular and persistent Hole Punch cloud formed over Mobile, Alabama at lunchtime. Numerous curious people photographed it. The event was so much a topic of conversation that it was the top local news story of the day.