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Countless feather clouds

In the context of atmospheric processes initiated by air traffic, the formation of contrails from the exhaust plume of airplanes plays a prominent role, as this creates a new, completely artificial kind of high clouds. The importance of contrails and aircraft-induced clouds concerning their influence on atmospheric radiation fluxes is still under research, and therefore afflicted with uncertainties. As part of the dissertation by Simon Gruber, the high-resolution regional numerical model COSMO-ART, which is also used in operational weather forecasting, has been extended to include a parameterization that allows both the formation and the life cycle of contrails and contrails to be calculated. A two-moment scheme for cloud microphysics, augmented by a separate class for contrail ice, describes this life cycle. This is necessary to achieve a better description of the high ice crystal number concentrations occurring in contrails. The underlying set of input data contains spatially and temporally high-resolution flight trajectories over Central Europe and is derived from real-time data. The parameterization thus provides aircraft type dependent source terms for ice mass and number in contrails. A case study was conducted to investigate the influence of contrails and contrails on the shortwave radiation fluxes at the Earth's surface. This work, which was carried out together with the DLR, represents the first approach to close the gap between large-eddy simulations and climate studies. A special focus is put on the demonstration of an improved weather forecast with respect to predicting high-level cloudiness and the resulting radiative fluxes when including contrails and contrail cirrus. This is due to the improved model is able to simulate high clouds that would otherwise be missing. The effect of additional clouding reduces both incidental solar radiation on the ground and photovoltaic energy production by up to 10%.

Contact: Dr. Simon Gruber, Dr. Bernhard Vogel

Gruber, S., Unterstrasser, S., Bechtold, J., Vogel, H., Jung, M., Pak, H., Vogel, B. (2018): Contrails and their impact on shortwave radiation and photovoltaic power production - a regional model study, Atmos. Chem. Phys., 18, 6393-6411, Document