Numerical simulations of persistent contrails

Abstract

Numerical (2D) simulations of persistent contrails have been performed. The simulations begin in the vortex phase (i.e., when the aircraft wake dynamics are dominated by the pair of downward travelling vortices) and pursue the evolution for half an hour. Particular emphasis was laid on the mechanisms by which contrails expand to reach the large lateral dimensions often observed and on the ice production in these artificial clouds. Cross-sectional spreading rates are found to range from 120 to 290 m2 s-1. The expansion is mainly caused by the secondary and higher-order vortices that develop from the reaction of the atmosphere with the downward travelling pair of primary vortices that are themselves produced by the aircraft. An additional driving force for contrail expansion is the gravitational collapse that results from differences between the potential temperature profiles inside and outside the contrails. Humidity and temperature of the ambient air control the growth of the ice particles and, therefore, all those properties that depend on crystal size and the overall ice production rate. Radiative cooling and release of latent heat affect expansion rate or turbulence intensity only weakly, at least in the first 30 min.