Ash concentration of Sabancaya volcanic plumes retrieved from a 95 GHzradar and a disdrometer

International audienceWe have carried out an experiment using a 3.2 mm-wavelength scanning Doppler radar and a laser disdrometerto investigate ash plumes of Sabancaya volcano (Peru) in May 2018. Our main objectives were to retrieve themass loading parameters (concentration, mass flux) which are critical for the modelling of ash dispersal, as wellas to study the dimensions and internal dynamics of the eruptive columns, plumes and fallout. The radar andthe disdrometer were respectively located at 4.5 km NNE and 4.5 km E from the vent. Multiple radar soundingconfigurations were tested either in fixed-pointing mode, generally close to the source, or using scans acrossvarious regions of the plumes.Particle Size Distribution, shapes and density were characterized from microphysical analyses, sieving and waterpycnometry of ash samples collected on the ground. A Parsivel2 disdrometer also recorded the sizes, and settlingvelocities of fallout, allowing us to estimate sedimentation rates on the ground and to derive an empirical lawrelating calculated ash concentrations and reflectivities. Comparing the latter with reflectivities measured by theradar at unprecedented space-time resolutions (down to 12.5 m and 0.25 s) allowed us to obtain the internal massdistribution of eruptive columns, plumes, and fallout at various distances from the emission source