Volcanic Emissions, Plume Dispersion and Downwind Radiative Impacts
following Mount Etna Series of Eruptions of 21-26 February 2021
Abstract
During the extended activity of Mount Etna volcano in February-April
2021, three distinct paroxysmal events took place from 21 to 26
February, which were associated with a very uncommon transport of the
injected upper-tropospheric plumes towards the north. Using a synergy of
observations and modelling, we characterised the emissions and
three-dimensional dispersion for these three plumes, we monitor their
downwind morphological and optical properties, and we estimate their
radiative impacts at selected locations. With a satellite-based source
inversion, we estimate the emitted sulphur dioxide (SO2) mass at an
integrated value of 55 kt and plumes injections at up to 12 km
altitudes, which combine to qualify this series as extreme in the
eruption strengths spectrum for Mount Etna. We then combine Lagrangian
dispersion modelling, initialised with measured temporally-resolved SO2
emission fluxes and altitudes, with satellite observations to track the
dispersion of the three individual plumes. The transport towards 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 in the visible spectral range ranging from about 0.004 to 0.03
and local daily average shortwave radiative forcing ranging from about
-0.2 to -1.2 W/m2 (at the top of atmosphere) and from
about -0.2 to -3.5 W/m2 (at the surface) are found.
Both the aerosol optical depth and the radiative forcing of the plume
depends strongly on its morphology (position of the sampled section of
the plume) and composition (possible presence of fine ash).