Aerosol variability over oceans using micro-pulse lidar and photometer: Insights from TRANSAMA ship-based campaign

International audience Abstract. The TRANSAMA campaign (Transit to AMARYLLIS-AMAGAS oceanographic cruise), conducted aboard the research vessel Marion Dufresne II investigated aerosol properties during its transit from La Reunion Island to Barbados (April–May 2023). A set of remote sensing instruments, including two CE318-T Sun-sky-lunar photometers and a CE370 single-wavelength elastic lidar, was deployed under the MAP-IO (Marion Dufresne Atmospheric Program–Indian Ocean) framework. Synergistic observations provided vertically resolved aerosol properties, such as extinction coefficients, alongside atmospheric structure, highlighting the marine boundary layer (MBL) top at 800 ± 300 m. While the photometer observations revealed very clean atmospheric conditions over the South Atlantic (AOD(440) = 0.08 ± 0.04), thin aerosol layers above the MBL were identified as long-range transported residual biomass-burning-urban aerosols from Southern Africa with effective LR of 33 ± 12 sr. Cloud layers covering a large range of altitudes (up to 16 km) were observed in 53 % of the lidar profiles with higher occurrence in low altitudes where the aerosol content was higher. These findings emphasize the impact of continental aerosols on remote oceanic regions, with implications on cloud formation and climate processes. The campaign also facilitated performance assessments of the deployed instrumentation, supporting the development of advanced mobile observatories for coupled lidar-photometer systems in marine environments.