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This paper presents model validation results for the latest version release of the FALL3D atmospheric transport model. The code has been redesigned from scratch to incorporate different categories of species and to overcome legacy issues that precluded its preparation towards extreme-scale computing. The model validation is based on the new FALL3D-8.0 test suite, which comprises a set of four real case studies that encapsulate the major features of the model; namely, the simulation of long-range fine volcanic ash dispersal, volcanic SO 2 dispersal, tephra fallout deposits and the dispersal and deposition of radionuclides. The first two test suite cases (i.e. the June 2011 Puyehue-Cordón Caulle ash cloud and the June 2019 Raikoke SO 2 cloud) are validated against geostationary satellite retrievals and demonstrate the new FALL3D data insertion scheme. The metrics used to validate the volcanic ash and SO 2 simulations are the structure, amplitude and location (SAL) metric and the figure of merit in space (FMS). The other two test suite cases (i.e. the February 2013 Mt. Etna ash cloud and associated tephra fallout deposit, and the dispersal of radionuclides resulting from the 1986 Chernobyl nuclear accident) are validated with scattered ground-based observations of deposit load and local particle grain size distributions and with measurements from the Radioactivity Environmental Monitoring database. For validation of tephra deposit loads and radionuclides, we use two variants of the normalised root-mean-square error metric. We find that FALL3D-8.0 simulations initialised with data insertion consistently improve agreement with satellite retrievals at all lead times up to 48 h for both volcanic ash and SO 2 simulations. In general, SAL scores lower than 1.5 and FMS scores greater than 0.40 indicate acceptable agreement with satellite retrievals of volcanic ash and SO 2. In addition, we show very good agreement, across several orders of magnitude, between the model and observations for the 2013 Mt. Etna and 1986 Chernobyl case studies. Our results, along with the validation datasets provided in the publicly available test suite, form the basis for future improvements to FALL3D (version 8 or later) and also allow for model intercomparison studies. [ABSTRACT FROM AUTHOR]

This manuscript presents different application cases and validation results of the latest version release of the FALL3D-8.0 model, an open-source atmospheric transport model. The code has been redesigned from scratch to incorporate different categories of species and to overcome legacy issues that precluded its preparation towards extreme-scale computing. Validation results are shown for long-range dispersal of fine volcanic ash and SO2 clouds, tephra fallout deposits and dispersal and ground deposition of radionuclides. The first two examples (i.e. the 2011 Puyehue-Cordón Caulle and 2019 Raikoke eruptions) make use of geostationary satellite retrievals for two purposes: first, to furnish an initial data insertion condition for the model; and second, to validate the time series of model outputs against the satellite retrievals. The metrics used to validate the model simulations of volcanic ash and SO2 are the Structure, Amplitude and Location (SAL) metric and the Figure of Merit in Space (FMS). The other two application cases are validated with scattered ground-based observations of deposit load and local particle grain size distributions from the 23 February 2013 Mt. Etna eruption and with measurements from the Radioactivity Environmental Monitoring (REM) database during the 1986 Chernobyl nuclear accident. Simulation results indicate that FALL3D-8.0 outperforms previous code versions both in terms of model accuracy and code performance. We also find that simulations initialised with the new data insertion scheme consistently improve agreement with satellite retrievals at all lead times out to 48 hours for both SO2 and long-range fine ash simulations. [ABSTRACT FROM AUTHOR]

This paper presents FALL3D-8.0, the last version release of an open-source code with 15+ years of track record and a growing number of users in the volcanological and atmospheric communities. The code has been redesigned and rewritten from scratch in the framework of the EU Centre of Excellence for Exascale in Solid Earth (ChEESE) in order to overcome legacy issues and allow for successive optimisations in the preparation of the code towards extreme-scale computing. However, this baseline version already contains substantial improvements in terms of model physics, solving algorithms, and code accuracy and performance. The code, originally conceived for atmospheric dispersal and deposition of tephra particles, has been extended to model other types of particles, aerosols and radionuclides. The solving strategy has also been changed, replacing the former central-difference scheme for a high-resolution central-upwind scheme derived from finite volumes, which minimises numerical diffusion even in the presence of sharp concentration gradients and discontinuities. The parallelisation strategy, input/output (I/O), model pre-process workflows and memory management have also been reconsidered, leading to substantial improvements on code scalability, efficiency and overall capability to handle much larger problems. All these new features and improvements have implications on operational model performance and allow, among others, adding data assimilation and ensemble forecast in future releases. This paper details the FALL3D-8.0 model physics and the numerical implementation of the code. [ABSTRACT FROM AUTHOR]

This manuscript presents FALL3D-8.0, the last version release of an open-source code with 15+ years of track record and a growing number of users in the volcanological and atmospheric communities. The code has been redesigned and rewritten from scratch in the framework of the EU Center of Excellence for Exascale in Solid Earth (ChEESE) in order to overcome legacy issues and allow for successive optimisations that are already planned in the preparation of the code towards extreme-scale computing. However, this baseline version already contains substantial improvements in terms of model physics, solving algorithms, and code accuracy and performance. The code, originally conceived for atmospheric dispersal and deposition of tephra particles, has been extended to model other types of particles, aerosols and radionuclides. The solving strategy has also been changed, replacing the former central-differences scheme for a high-resolution central-upwind scheme derived from finite volumes, which minimises numerical diffusion even in presence of sharp concentration gradients and discontinuities. The parallelisation strategy, Input/Output (I/O), model pre-process workflows and memory management have also been reconsidered, leading to substantial improvements on code scalability, efficiency, and overall capability to handle much larger problems. This paper details the FALL3D-8.0 model physics and the numerical implementation of the code. [ABSTRACT FROM AUTHOR]

FALL3D-8.0 is the new release of the FALL3D model (Folch et al., 2009;doi:10.1016/j.cageo.2008.08.008), a three-dimensional time-dependent Eulerian model foratmospheric transport and deposition based on the advection–diffusion–sedimentationequation (Folch et al., 2009; doi:10.1016/j.cageo.2008.08.008). The model upgradeincorporates dramatic improvements both in terms of physics and numerical algorithms andperformance. In terms of model physics, the original tephra transport model has beenextended to include mineral dust, radionuclides, and chemistry of SO2. Besides theexisting models describing phenomena such as particle resuspension, volcanic plumes,gravity spreading in the umbrella region, particle size distribution, and particleaggregation, different new parameterizations have also been introduced in order todescribe eddy diffusivity, dry and wet deposition, and transport of radionuclides.In terms of numerical algorithms and performance, FALL3D-8.0 uses a verticalσ-coordinate to better capture local terrain effects, a Runge-Kutta forth-order intime explicit scheme, and a much more efficient high-resolution central-upwindscheme (Kurganov and Tadmor, 2000; doi:10.1006/jcph.2000.6459). The MPI-basedparallelization of the code, written in FORTRAN 90, has also been reformulated in order todramatically increase its performance on Petascale machines, including a better domaindecomposition, parallel I/O, a parallel preprocess in which coupling with multiple drivingmeteorological models has been made more efficient, and a better memory management toreduce communications and improve code scalability. A few examples for differentkind of applications are presented and the improve in code performance discussed. [ABSTRACT FROM AUTHOR]