Occurrence of embedded contrails in cirrus clouds observed with the HALO research aircraft

Aviation affects the Earth’s energy balance through both non-CO2 effects and exhaust gases and soot emissions. One such effect is the formation of contrails, which can alter the climate impact of cirrus clouds and their optical and microphysical properties. In this study, embedded contrails were detected during active remote sensing observations with the German research aircraft HALO. Using observations during ML-CIRRUS, it is found that embedded contrails can be identified in WALES lidar measurements through particle backscatter coefficients larger than 4 Mm⁻¹ sr⁻¹ and particle linear depolarization ratios (PLDR) below 30% and 43% for clouds with low and high mean PLDR, respectively. The thus identified contrail-affected lidar and lidar-radar measurements during ML-CIRRUS and other HALO campaigns will be used to assess the impact of contrails that form in already existing cirrus clouds on the optical and microphysical properties of those clouds, and in how far potential affects might also be detected in spaceborne lidar observations.