Estimation of optical and microphysical characteristics of contrails using Lidar at SIRTA observatory, Paris

Contrails are local and thin anthropogenic clouds that are difficult to predict by numerical weather forecasting models. Given their local radiative impact, it is urgent to properly document their characteristics in order to improve their parametrization in weather models and evaluate their contribution to global warming. In the framework of the Climaviation project (Funded by the French Direction Générale de l’Aviation Civile (DGAC)), this study aims to quantify the optical, geometrical and microphysical characteristics of contrails at the SIRTA observatory in Palaiseau, France. We used a co-localised instrumental synergy composed of the Lidar IPRAL (a multichannel raman Lidar), a total sky camera, and aircraft flight altitudes to detect the occurrence of contrails over the site during the 2018-2023 period. Based on three (3) case studies, the particular and molecular integration methods are applied on the Lidar backscatter, to estimate the optical depth of contrails. Vertical profiles of temperature and relative humidity from Trappes radiosoundings are used to characterize the atmospheric conditions classified into three (3) categories of contrail evolution (non-persistent, persistent, and spreading). The results show that the optical thickness of contrails can reach 0.3 for contrails formed in a thick persistent layer. It is lower for contrails developing in a non-persistent layer. During daytime, the contrails contribute to reducing the surface downwelling and upwelling measured shortwave radiation in the order of 218 and 50 W m^-2 respectively. Their impact on longwave radiation is relatively negligible.