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Abstract. Lineshaped contrails were detected with the research aircraft Falcon during the CONCERT -CONtrail and Cirrus ExpeRimenT -campaign in October/November 2008. The Falcon was equipped with a set of instruments to measure the particle size distribution, shape, extinction and chemical composition as well as trace gas mixing ratios of sulfur dioxide (SO 2 ), reactive nitrogen and halogen species (NO, NO y , HNO 3 , HONO, HCl), ozone (O 3 ) and carbon monoxide (CO). During 12 mission flights over Europe, numerous contrails, cirrus clouds and a volcanic aerosol layer were probed at altitudes between 8.5 and 11.6 km and at temperatures above 213 K. 22 contrails from 11 different aircraft were observed near and below ice saturation. The observed NO mixing ratios, ice crystal and soot number densities are compared to a process based contrail model. On 19 November 2008 the contrail from a CRJ-2 aircraft was penetrated in 10.1 km altitude at a temperature of 221 K. The contrail had mean ice crystal number densities of 125 cm −3 with effective radii r eff of 2.6 µm. The presence of particles with r>50 µm in the less than 2 min old contrail suggests that natural cirrus crystals were entrained in the contrail. Mean HONO/NO (HONO/NO y ) ratios of 0.037 (0.024) and the fuel sulfur conCorrespondence to: C. Voigt (christiane.voigt@dlr.de) version efficiency to H 2 SO 4 ( S↓ ) of 2.9 % observed in the CRJ-2 contrail are in the range of previous measurements in the gaseous aircraft exhaust. On 31 October 2010 aviation NO emissions could have contributed by more than 40% to the regional scale NO levels in the mid-latitude lowest stratosphere. The CONCERT observations help to better quantify the climate impact from contrails and will be used to investigate the chemical processing of trace gases on contrails.

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Aircraft wake vortex evolution in ground proximity is investigated numerically with large eddy simulations (LES). The simulations are performed with different modifications of the ground surface in order to trigger rapid vortex decay or to simulate the landing of an aircraft. The impact of environmental turbulence in terms of turbulent winds is taken into account, where wall-resolved and wall-modeled LES are performed for low and high Reynolds number cases, respectively. In order to understand wake vortex decay mechanisms in ground proximity the interaction of primary and secondary vortices is thoroughly investigated. The results show that vortex decay is initiated and accelerated with obstacles at the ground. In order to optimize obstacle shape and size we show that we can achieve a similar effect with relatively small plates as with large block-shaped barriers. Concerning large Reynolds numbers we show that turbulence effects triggered by the ground can not be modeled by a simple wall model. As a first approximation of landing we use a ramp at the ground and show that the flow disturbances are similar to the result of flat ground with obstacles. In particular two kinds of so-called end effects are superposed: pressure waves in the vortex core and the propagation of the secondary vortex structures.

Large-eddy simulations of a coherent counter-rotating vortex pair in different environments are performed. The environmental background is characterized by varying turbulence intensities and stable temperature stratifications. Turbulent exchange processes between the vortices, the vortex oval, and the environment, as well as the material redistribution processes along the vortex tubes are investigated employing passive tracers that are superimposed to the initial vortex flow field. It is revealed that the vortex bursting phenomenon, known from photos of aircraft contrails or smoke visualization, is caused by collisions of secondary vortical structures traveling along the vortex tube which expel material from the vortex but do not result in a sudden decay of circulation or an abrupt change of vortex core structure. In neutrally stratified and weakly turbulent conditions, vortex reconnection triggers traveling helical vorticity structures which is followed by their collision. A long-lived vortex ring links once again establishing stable double rings. Key phenomena observed in the simulations are supported by photographs of contrails. The vertical and lateral extents of the detrained passive tracer strongly depend on environmental conditions where the sensitivity of detrainment rates on initial tracer distributions appears to be low.