Dispersion Strengths & Weaknesses

Analysis Strengths & Weaknesses and link with the other WP

As illustrated below, gathering complementary observations, modelling capabilities and expertise from both atmospheric/climate sciences and volcanological communities is critical to reach these goals, which requires to fill the following scientific gaps:

(i) When a volcano is instrumented on the ground, methods developed in WP1 and WP2 can provide high spatial and temporal information on the volcanic source. In this perspective, advances have been made for the characterization of small, basaltic plumes (Harris et al. 2013; Barnie et al. 2015; Gurioli et al. 2013; 2014; Leduc et al. 2015; Bombrun et al. 2015, Gurioli et al; 2015). However, such ground-based methods, if not destroyed during the eruption, can be hampered when the volcanic activity becomes intense. In this context, while today less sensitive than ground-based observations, the exploitation of satellite observations (passive radiometers and spectrometers, space LiDAR) of volcanic gas/particle plumes can be used. Broad-band sensors onboard geostationary satellites (e.g. SEVIRI) bring information on the volcanic source and atmospheric evolution of the effluents (see, e.g. Sellitto et al., 2017c) at typically sub-hourly temporal resolution. However, the low spectral resolution and subsequent low sensitivity of these sensors do not generally allow a refined estimation of source parameters. In complement, gas/particle spaceborne imagery from high spectral resolution sensors (e.g. IASI, OMI, OMPS) is used. The joint exploitation of these plume satellite observations through inverse modeling procedures that involve the use of a mesoscale chemistry-transport model, can provide complementary hourly-resolved characterization of the volcanic gas/ash source (in terms of both flux and altitude) (see, e.g. Boichu et al., 2015). Forthcoming spaceborne sensors show increasing spatial and spectral resolutions (see, e.g. Crevoisier et al., 2014) which should provide a better monitoring of volcanic activity of low intensity. In order to benefit from this progress, setting a protocol for building a single standardized database (link with WP1, WP2 and WP4), gathering ground- and satellite-derived information on the volcanic source, would be highly valuable to be able to describe the whole range of volcanic emissions.

(ii) understand how physical-and-chemical process such as nucleation, coagulation, condensation and solid/liquid particle aggregation, as well as particles properties like shape and density, can influence dispersion, sedimentation, dry and wet removal (in particular, in presence of complex gaseous and solid/liquid plume mixtures), as well as external factors such as the presence of important topography (for proximal-to-medial distances), or the presence of marine compounds (sea salt, organics, halogens, DMS) and other pollutants (gaseous or particulate anthropic pollution, mineral dust, etc), can interact with and modify these processes.

(iii) the identification of specific tracers to track and detect volcanic plume dispersion, that may help in singling out their downwind impacts, especially when in complex environments in terms of co-existent aerosol sources.

(iv) the improvement of the knowledge of direct and indirect climate forcing of volcanic plumes, in particular for continuous weak minor volcanism. In particular, volcanic emission-clouds-climate processes (indirect effects), including microphysical processes connecting gas emissions to secondary aerosols and then to liquid water and/or ice nucleation, is not yet sufficiently known in terms of fundamental processes. The long-term quantification of regional climate forcing of test volcanoes, as well as their interactions with different environments (mediterranean, tropical,…) will be addressed by this WP.

(v) a clarification of other radiative impacts of volcanic plumes, e.g. diabatic heating/cooling rates associated with interactions radiation-plume, that can modify the vertical atmospheric dynamics, with feedbacks on plume dispersion, or the impact of volcanic plumes to air quality by the perturbation of lower tropospheric photochemistry.

(vi) a better quantification of direct air quality and environmental impacts, like local to regional surface pollution enhancements by volcanic emissions or acid rain produced by wet deposition of acid aerosols of volcanic origin. Also, volcanic halogen chemistry may induce/enhance deposition of mercury.

(vii) a study of the impact of volcanic emissions on 3D atmospheric composition, at short and long time scales. In particular, the fate of volcanic halogen compounds is still to be addressed: what is their contribution to the stratospheric halogen burden and to the evolution of the ozone layer? Through which processes? Which impact on sulphate aerosols formation/evolution and radiative impacts? More generally, the chemical interaction of volcanic emissions with their environment may have consequences on ozone and aerosols, from the vicinity of the volcano to the global scale.

(viii) a parameterization of the volcanic plume in its three dimensions (thickness, lateral spreading, dispersion) from proximal (WP2) to distal locations, its concentration and particle size distribution variations in space and time (especially for aviation purposes). All of these developments have the objective of improving our knowledge on, and allowing mitigation of the impact of, volcanic plumes at different atmospheric levels. This is why it is fundamental to merge all communities that can share knowledge, measurements and tools to combine and integrate approaches so as to achieve a complete picture of the phenomena. This includes connecting research communities with operational hazard prediction such as the Volcanological Observatories and the VAAC.