Aerosol Characterization of the Stratospheric Plume From the Volcanic Eruption at Hunga Tonga 15 January 2022

Following the Hunga Tonga eruption (20.6 degrees S, 175.4 degrees W, mid-January 2022), we present a balloon-borne characterization of the stratospheric aerosol plume one week after its injection (on 23 and 26 January 2022, La Reunion island at 21.1 degrees S, 55.3 degrees E). Satellite observations show that flight (a) took place during the overpass of a denser plume of sulfate aerosols (SA) compared to a more diluted plume during flight. (b) Observations show that the sampled plumes (at around 22, 25 and 19 km altitude, respectively) consist exclusively of very small particles (with radius <1 mu m). Particles with radii between 0.5 and 1.0 mu m show optically transparent features pointing to predominant SA. Particles with radii below 0.5 mu m are partly absorbing, which could point to small sulfate coated ash particles, a feature not identified with space-borne observations. This shows that in situ observations are necessary to fully characterize the microphysical properties of the plumes tracked by space-borne instruments.