Properties of In-cirrus Contrails from Airborne Remote-sensing Data (PICARD)

• Applicant: Dr. Matthias Tesche
• Subject Area: Atmospheric Science
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 520829878

Aviation affects the Earth's energy balance through the emission of exhaust gases and a variety of non-CO2 effects of which linear contrails are the best known. Contrails form from aircraft effluent, can develop into widespread and persistent contrail cirrus, and affect the occurrence rate of cirrus. While optically thick cirrus can have a net cooling effect on the atmosphere, optically thin cirrus generally causes warming. Aircraft emissions and contrails can lead to optically thin and thick cirrus. Aircraft that fly through already existing cirrus can lead to contrails that are embedded in those clouds. Such embedded contrails could alter cirrus properties to a degree that inverts its climate effect from net warming to net cooling. Today, the effect of embedded contrails on the properties of already existing cirrus clouds is still virtually unstudied due to a lack of direct measurements and subsequent modelling studies. Only two observational studies have looked at the issue. Tesche et al. (2016) used spaceborne lidar data to show that embedded contrails increase the optical thickness of pre-existing cirrus. Marjani et al. (2022) found that ice crystal number concentration increases in cirrus regions that are affected by passing aircraft from analysing combined lidar-radar retrievals for the cases of Tesche et al. (2016). PICARD will expand upon the earlier work by exploiting the higher spatio-temporal resolution and measurement sensitivity of airborne lidar and radar measurements compared to spaceborne observations with the same measurement techniques. Observations of cirrus clouds conducted during at least four measurement campaigns with the German research aircraft HALO in regions where aircraft are likely to pass through already existing cirrus clouds will be analysed for serendipitous observations of embedded contrails. Lidar measurements during the dedicated cirrus experiments ML-CIRRUS and CIRRUS HL will be used to develop, test, and verify a mask for detecting perturbations in cirrus clouds that can be related to the passage of individual aircraft. The mask will be applied to those observations as well as the combined lidar-radar observations during NARVAL 1 and NAWDEX. The thus compiled data set will be used to quantify the effect of embedded contrails on the optical (lidar) and microphysical (lidar-radar) properties of pre-existing cirrus by relating changes in identified features to the unperturbed cloud. The data base of embedded contrails in HALO measurements will be used to establish a reference data set for the high-resolution modelling of embedded contrails, which is still in its infancy. The research proposed here is therefore vital in bounding the climate effect of aviation in light of steadily increasing flight numbers and mankind’s urge for global mobility.

• DFG Programme: Research Grants