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Modelling atmospheric dispersal of volcanic ash and aerosols is becoming increasingly valuable for assessing the potential impacts of explosive volcanic eruptions on buildings, air quality, and aviation. Management of volcanic risk and reduction of aviation impacts can strongly benefit from quantitative forecasting of volcanic ash. However, an accurate prediction of volcanic aerosol concentrations using numerical modelling relies on proper estimations of multiple model parameters which are prone to errors. Uncertainties in key parameters such as eruption column height and physical properties of particles or meteorological fields represent a major source of error affecting the forecast quality. The availability of near-real-time geostationary satellite observations with high spatial and temporal resolutions provides the opportunity to improve forecasts in an operational context by incorporating observations into numerical models. Specifically, ensemble-based filters aim at converting a prior ensemble of system states into an analysis ensemble by assimilating a set of noisy observations. Previous studies dealing with volcanic ash transport have demonstrated that a significant improvement of forecast skill can be achieved by this approach. In this work, we present a new implementation of an ensemble-based data assimilation (DA) method coupling the FALL3D dispersal model and the Parallel Data Assimilation Framework (PDAF). The FALL3D+PDAF system runs in parallel, supports online-coupled DA, and can be efficiently integrated into operational workflows by exploiting high-performance computing (HPC) resources. Two numerical experiments are considered: (i) a twin experiment using an incomplete dataset of synthetic observations of volcanic ash and (ii) an experiment based on the 2019 Raikoke eruption using real observations of SO2 mass loading. An ensemble-based Kalman filtering technique based on the local ensemble transform Kalman filter (LETKF) is used to assimilate satellite-retrieved data of column mass loading. We show that this procedure may lead to nonphysical solutions and, consequently, conclude that LETKF is not the best approach for the assimilation of volcanic aerosols. However, we find that a truncated state constructed from the LETKF solution approaches the real solution after a few assimilation cycles, yielding a dramatic improvement of forecast quality when compared to simulations without assimilation., This research has been partially funded by the H2020 Center of Excellence for Exascale in Solid Earth (ChEESE) under the grant agreement no. 823844.

The new version of FALL3D has recently been released with several new features and improvements in model physics, solving algorithms, code accuracy and performance [1]. Among the new features are a data insertion scheme and the ability to simulate volcanic SO2 clouds. The data insertion scheme enables users to initialise model runs from satellite retrievals. This modelling approach is useful for removing uncertainties associated with source term parameters such as the mass flow rate, plume height, source duration and start time. Here we demonstrate and validate the new data insertion scheme in FALL3D-8.0 using geostationary satellite retrievals of volcanic ash and SO2.

Ash emitted during explosive volcanic eruptions may disperse over vast areas of the globe posing a threat to human health and infrastructures and causing significant disruption to air traffic. In Antarctica, at least five volcanoes have reported historic activity. However, no attention has been paid to the potential socio-economic and environmental consequences of an ash-forming eruption occurring at high southern latitudes. This work shows how ash from Antarctic volcanoes may pose a higher threat than previously believed. As a case study, we evaluate the potential impacts of ash for a given eruption scenario from Deception Island, one of the most active volcanoes in Antarctica. Numerical simulations using the novel MMB-MONARCH-ASH model demonstrate that volcanic ash emitted from Antarctic volcanoes could potentially encircle the globe, leading to significant consequences for global aviation safety. Results obtained recall the need for performing proper hazard assessment on Antarctic volcanoes, and are crucial for understanding the patterns of ash distribution at high southern latitudes with strong implications for tephrostratigraphy, which is pivotal to synchronize palaeoclimatic records., A.G. thanks the support provided by the Ramón y Cajal research program (RYC-2012-11024). This research was partially funded by the MINECO grants VOLCLIMA (CGL2015-72629-EXP) and POSVOLDEC(CTM2016- 79617-P)(AEI/FEDER-UE)

Impacts of explosive volcanic eruptions on civil aviation were reconsidered after the 2010 Eyjafjallajokull eruption in Iceland, which caused unprecedented disruptions of air traffic operations in Europe. During and after the aviation breakdown of April–May 2010, communication between the involved stakeholders was recognized as a major concern. Due to the complexity and multidisciplinary nature of the topic, a great number of actors are involved, which often have little interaction outside these exceptional events. In this work, we aim at identifying the relationships between the stakeholders involved in aviation management during eruptions, as well as their needs and priorities. We perform an anonymous on-line survey, focused mainly on the use of tephra dispersal models for civil aviation purposes. We collect feedback on recent developments including our current impact assessment research, which produced a GIS-based software tool to estimate impacts on aviation based on tephra dispersal forecasts. Answers allow identifying stakeholders' requirements on ash dispersal forecasts and their use for aviation management purposes. We underline the main differences between three homogeneous groups (aviation managers and employees, modellers and field scientists, other stakeholders) and identify main end-user requirements for developing tools similar to ours. This work provides useful insights for the development of tools to support aviation stakeholders during volcanic eruptions.

We present a methodology to estimate the impacts of volcanic ash dispersal on civil avia- tion and a software tool aimed at assisting air traffic management in the event of ash-con- taminated airspace. The tool merges atmospheric dispersal model forecasts with air traffic data in a map-based platform to produce tables and maps showing potentially affected air- ports, flights and airspace sectors. Impacts can be estimated based on user-defined ash con- centration thresholds, or on the amount of ash potentially ingested by airplanes flying through diluted ash clouds. The impact can be assessed on single Flight Level (FL) slabs, or across the whole vertical airspace. The procedure is automated within a Geographical Information System (GIS). For illustrative purposes, we estimate the potential impacts on the European air traffic of an eruption from Katla volcano in Iceland, assuming a ‘‘worst- case’’ meteorological scenario. We compare the capabilities of the tool with those of similar existing software and justify our design choices. Finally, we discuss the use of the tool in current and future air traffic management strategies during explosive volcanic eruptions.