Three-dimensional Large Eddy Simulations of contrail ice crystal formation with an improved representation of aerosol and ice microphysics

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Contrail cirrus (consisting of young and aged contrails) are the largest known contributor to the anthropogenic global warming caused by aviation. The number of formed contrail ice crystals, which is particularly determined by engine soot number emissions and atmospheric conditions, can have a strong influence on the further contrail cirrus life cycle, properties and their radiative impact.So far, there are two complementary approaches to simulate the formation of contrails during the jet phase. While current 3D studies focus on the jet dynamics, the previous 0D approaches concentrate on microphysical processes in the jet plume. The basic objective of this project is to combine the benefits of these two approaches which means to simulate contrail formation behind commercial aircraft by means of three-dimensional Large Eddy Simulations (LES) with an improved representation of contrail ice microphysics. Concerning the model development, the Lagrangian Ice Microphysics (LCM) code, originally developed for natural ice clouds, has to be extended by the contrail ice crystal formation and coupled to an up-to-date EULAG version that supports compressible flow phenomens. One main goal of the 3D LES is to analyze the spatial and temporal evolution of the ice crystal formation in the exhaust plume for different atmospheric conditions where contrails can form. Thereby, the entrainment of upper tropospheric background aerosol particles, which also can form ice crystals in the plume, will be considered for the first time in a 3D model. Based on the LES calculations, a heuristic parameterization for the formation of contrail ice crystals will be derived and integrated into the global climate model ECHAM5. This should be linked with an already existing parameterization of the ice crystal loss during the vortex phase in order to improve the initialization of contrails in the climate model. Within the global simulations, both parametrized processes and their effects on contrail cirrus properties dependent on different meteorological conditions will be investigated in more detail. Finally, an important objective is to analyze the influence of reduced soot number emissions (as they can be realized by the use of alternative fuel blends in cruise flight) on the formation of contrail ice crystals and, within the global climate model, to investigate this influence on contrail cirrus properties and their climate impact.