Optical properties and global distribution of the Hunga aerosols 2022 observed by Aeolus and atmospheric lidars: new insights into the vertical sedimentation of stratospheric sulfate plumes

Abstract. Stratospheric aerosol plumes from the 2022 Hunga eruption were observed by the first-ever ultraviolet (UV) 355 nm Doppler and High Spectral Resolution Lidar (HSRL) on board the European Space Agency’s Aeolus satellite. Independent measurement of extinction and co-polarized backscatter coefficients for particles are shown, capturing the Hunga plumes up to ≈ 28 km in altitude. Global map of L2A product are produced for latitudes band up to [35° S–10° N]. They are analysed with sulphur dioxide (SO₂) concentration and sulfate aerosol (SA) optical depth (OD). A plume composed of optically thick patches with high SA OD above 0.025 is captured above 26 km in altitude. It exhibits high UV signal extinction up to 350 Mm⁻¹, scattering ratio (SR) up to 40, local optical depth (LOD) above 0.2, and lidar ratio (LR) above 100 sr. These SA long-lived patches are observed drifting south and transported west. Two branches separate by mid February 2022: a southern tale at ≈ 25 to 27 km in altitude around latitudes [30° S–15° S] and a northern tale at ≈ 23 to 25 km in altitude around latitudes [15° S–10° N]. The LR and LOD measured by Aeolus for the ageing branches reveal lower values below 80 sr and 0.04 respectively. A short-lived plume with low SA OD and high SO₂ concentration is observed at lower altitudes ≈ 18 to 22 km with less strong UV scattering properties, and appears to disaggregate quickly.