Volcanic Emissions, Plume Dispersion, and Downwind Radiative Impacts Following Mount Etna Series of Eruptions of February 21-26, 2021

During the extended activity of Mount Etna volcano in February-April 2021, three distinct paroxysmal events took place from February 21 to 26, which were associated with a very uncommon transport of the injected upper-tropospheric plumes toward the north. Using a synergy of observations and modeling, we characterized the emissions and three-dimensional dispersion for these three plumes, monitored their downwind distribution and optical properties, and estimated their radiative impacts at selected locations. With a satellite-based source inversion, we estimate the emitted sulfur dioxide (SO2) mass at an integrated value of 55 kt and plumes injections at up to 12 km altitudes, which qualifies this series as an extreme event for Mount Etna. Then, we combine Lagrangian dispersion modeling, initialized with measured temporally resolved SO2 emission fluxes and altitudes, with satellite observations to track the dispersion of the three individual plumes. The transport toward the north allowed the height-resolved downwind monitoring of the plumes at selected observatories in France, Italy, and Israel, using LiDARs and photometric aerosol observations. Volcanic-specific aerosol optical depths (AODs) in the visible spectral range ranging from about 0.004 to 0.03 and local daily average shortwave radiative forcing (RF) ranging from about -0.2 to -1.2 W m(-2) (at the top of atmosphere) and from about -0.2 to -3.0 W m(-2) (at the surface) are found. The composition (possible presence of ash), AOD, and RF of the plume have a large inter-plume and intra-plume variability and thus depend strongly on the position of the sampled section of the plumes.