Statistical analysis of contrail to cirrus evolution during the Contrail and Cirrus Experiment (CONCERT)

Air traffic affects the cloudiness, and thus the climate, by emitting exhaust gases and particles. The study of the evolution of contrail properties is very challenging due to the complex interplay of vortex dynamics and atmospheric environment (e.g. temperature, supersaturation). Despite substantial progress in recent years, the optical, microphysical, and macrophysical properties of contrails and ambient cirrus during contrail formation and subsequent ageing are still subject to large uncertainties due to instrumental and observational limitations and the large number of variables influencing the contrail life cycle. In this study, various contrail cases corresponding to different aircraft types and atmospheric conditions are investigated using a statistical method based on the in situ optical measurements performed during the CONCERT campaigns 2008 and 2011. These two aircraft campaigns encompass more than 17 aircraft contrail cases. A Principal Component Analysis (PCA) of the angular scattering coefficients measured by the Polar Nephelometer has been implemented in order to classify the sampled ice cloud measurements in 6 clusters representative of different development stages of the contrails (primary wake, young contrail, contrail-cirrus and natural cirrus). Based on the information derived from air traffic control, extinction coefficients, asymmetry coefficients, nitrogen oxide concentrations, relative humidity with respect to ice (RHI) and particle size distributions are analyzed for each cluster to provide a characterization of the evolution of ice-cloud properties during the contrail to cirrus evolution. The PCA demonstrates that contrail optical properties are well suited to identify and discriminate the different contrail growth stages and to provide an independent method for the characterization of the evolution of contrail properties.