Combining LIDAR, all-sky camera, and ECMWF-ERA5 reanalysis to investigate contrail formation and evolution over Clermont-Ferrand, France on June 2, 2023

Contrails formed by aircraft in the upper troposphere contribute to anthropogenic climate forcing. However, the conditions driving their formation and persistence remain incompletely understood. This study combines a ACTRIS/EARLINET ground-based LIDAR, all-sky camera imagery, ADS-B aircraft tracking, and ECMWF-ERA5 reanalysis to analyse contrails formation and evolution over Clermont-Ferrand, France, on June 2, 2023. Twelve contrails are documented throughout the day, including five persistent and seven non-persistent contrails. Persistent contrails formed at 10.36 km altitude or lower are observed under ice-supersaturated conditions (relative humidity with respect to ice, RHi > 105 %) and at temperatures between 217 and 223 K. Non-persistent contrails produced by higher altitudes aircrafts, are associated with lower RHi mostly below 100 % and colder temperatures (214–217 K). The horizontal persistent contrail widths range from 0.53 ± 0.10 to 1.60 ± 0.44 km (all-sky camera estimation) and 0.35 ± 0.14 to 1.90 ± 0.32 km (LIDAR estimation), and vertical extents varied from 340 ± 10 to 440 ± 20 m. The optical properties of these contrails have also been estimated by LIDAR. Aerosol backscatter coefficient vary from 0.02 to 0.05 km −1 sr −1 , scattering ratios from 8 to 20, volume linear depolarization from 0.13 to 0.24 and particle linear depolarization from 0.17 to 0.45. The maximum contrail observation duration by camera is 180 min. The study highlights the potential of ground-based remote sensing for contrail monitoring. • Contrail study based on LIDAR, all-sky images, ADS-B and ECMWF ERA5 data. • Twelve contrails were observed on June 2, 2023, over Clermont-Ferrand, France. • Persistent contrails formed below 10.36 km in ice-supersaturated and cold air. • Non-persistent contrails occurred at higher altitudes in colder and dryer air. • Contrail widths reached up to 1.9 km and vertical extents up to 440 m.