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On the radiative forcing of volcanic plumes: modelling the impact of Mount Etna in the Mediterranean

Abstract : The impact of small to moderate volcanic eruptions on the regional to global radiative forcing and climate is still largely unknown and thought to be presently underestimated. In this work, daily average shortwave radiative forcing efficiencies at the surface (RFE Surf d), at top of the atmosphere (RFE TOA d) and their ratio (f), for upper tropospheric volcanic plumes with different optical characterization, are derived using the radiative transfer model UVSPEC and the LibRadtran suite. The optical parameters of the simulated aerosol layer, i.e., the Ångströem coefficient (α), the single scattering albedo (SSA) and the asymmetry factor (g), have been varied to mimic volcanic ash (bigger and more absorbing particles), sulphate aerosols (smaller and more reflective particles) and intermediate/mixed conditions. The characterization of the plume and its vertical distribution have been setup to simulate Mount Etna, basing on previous studies. The radiative forcing and in particular the f ratio is strongly affected by the SSA and g, and to a smaller extent by α, especially for sulphates-dominated plumes. The impact of the altitude and thickness of the plume on the radiative forcing, for a fixed optical characterization of the aerosol layer, has been found negligible (less than 1% for RFE Surf d , RFE TOA d and f). The simultaneous presence of boundary layer/lower tropospheric marine or dust aerosols, like expected in the Mediterranean area, modulates only slightly (up to 12 and 14% for RFE Surf d and RFE TOA d , and 3 to 4% of the f ratio) the radiative effects of the upper tropospheric volcanic layer.
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Pasquale Sellitto, Pierre Briole. On the radiative forcing of volcanic plumes: modelling the impact of Mount Etna in the Mediterranean. Annals of Geophysics, Istituto Nazionale di Geofisica e Vulcanologia (INGV), 2015, 58, ⟨10.4401/ag-6879⟩. ⟨hal-01277171⟩

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