Study of contrail microphysics in the vortex phase with a Lagrangian particle tracking model

Crystal sublimation/loss is a dominant feature of the contrail evolution during the vortex phase and has a substantial impact on the later contrail-to-cirrus transition. Previous studies showed that the fraction of crystals surviving the vortex phase depends primarily on relative humidity, temperature and the aircraft type. An existing model for contrail vortex phase simulations (with a 2-moment bulk microphysics scheme) was upgraded with a newly developed state-of-the-art microphysics module (LCM) which uses Lagrangian particle tracking. This allows for explicit process-oriented modelling of the ice crystal size distribution in contrast to the bulk approach. We show that it is of great importance to employ an advanced microphysics scheme to determine the crystal loss during the vortex phase. The LCM-model shows even larger sensitivities to the above mentioned key parameters than previously estimated with the bulk model. The impact of the initial crystal number is studied and for the first time also the initial width of the crystal size distribution. Both are shown to be relevant. This corroborates the need for a realistic representation of microphysical processes and knowledge of the ice phase characteristics. cirrus properties. Thus, in a first step Large Eddy Simulation models (LES) should be used to better understand the contrail-to-cirrus transition and quantify the dominant atmospheric and aircraft parameters affecting it. Recently, the transition of single contrails into a contrail-cirrus was extensively studied with a high resolution numerical model (Unterstrasser and Gierens, 2010a,b). Among other things these simulations revealed that the early contrail evolution during the jet and vortex phase affects the optical properties and the lifetime of the contrail-cirrus even hours later, emphasising the need for realistic vortex phase simulations.