Large-eddy simulation study of contrail microphysics and geometry during the vortex phase and consequences on contrail-to-cirrus transition

Large-eddy simulations (LES) with Lagrangian ice microphysics were used to study the early contrail evolution during the vortex phase. Microphysical and geometrical properties of a contrail produced by a large-sized aircraft (type B777/A340) were investigated systematically for a large parameter range. Crystal loss due to adiabatic heating in the downward moving vortices was found to depend strongly on relative humidity and temperature, qualitatively similar to previous 2-D simulation results. Contrail depth is as large as 450 m for the investigated parameter range and was found to be underestimated in a previous 2-D study. Further sensitivity studies show a nonnegligible effect of the initial ice crystal size distribution and the initial ice crystal number on the crystal loss, whereas the contrail structure and ice mass evolution is only barely affected by these variations. Variation of fuel flow has the smallest effect on crystal loss. At high supersaturations, our choice of contrail spatial initialization may underestimate the ice crystal loss. The set of presented sensitivity studies is a first step toward a quantitative description of young contrails in terms of vertical extent and crystal loss. Concluding contrail-to-cirrus simulations demonstrate the relevance of vortex phase processes and its three-dimensional modeling on the later contrail-cirrus properties.