Aerodynamic Contrails: Phenomenology and Flow Physics

Aerodynamic contrails have been recognized for a long time although they appear sporadically. Usually one observes them under humid conditions near the ground, where they are short-lived phenomena. Aerodynamic contrails appear also at cruise levels where they may persist when the ambient atmosphere is ice-supersaturated. The present paper presents a theoretical investigation of aerodynamic contrails in the upper troposphere. The required flow physics are explained and applied to a case study. Results show that the flow over aircraft wings leads to large variations of pressure and temperature. Average pressure differences between the upper and lower sides of a wing are on the order of 50 hPa, which is a quite substantial fraction of cruise-level atmospheric pressures. Adiabatic cooling exceeds 20 K about 2 m above the wing in a case study shown here. Accordingly, extremely high supersaturations (exceeding 1000%) occur for a fraction of a second. The potential consequences for the ice microphysics are discussed. Because aerodynamic contrails are independent of the formation conditions of jet contrails, they form an additional class of contrails that might be complementary because they form predominantly in layers that are too warm for jet contrail formation.