By Arnau Folch1, Antonio Costa2, Giovanni Macedonio2

1. Barcelona Supercomputing Center 2. Istituto Nazionale di Geofisica e Vulcanologia

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FALL3D (version 7.1) is a 3-D time-dependent Eulerian model for the transport and deposition of tephra developed in the framework of a collaboration between INGV and Barcelona Supercomputing Center (BSC). The model solves a set of advection-diffusion-sedimentation (ADS) equations on a structured terrain-following grid using a second-order Finite Differences (FD) explicit scheme. The model inputs are meteorological data, topography, vent coordinate, Eruption Source Parameters (ESP) such as column height, Mass Flow Rate (MFR), eruption duration, and Total Grain-Size Distribution (TGSD) which include particle shape and density information. Outputs are tephra ground load/thickness, airborne ash concentration and other related variables. The code, written in FORTRAN-90, is available for Unix/Linux/Mac X Operating Systems (OS) and can be compiled either as serial or parallel using MPI. A set of pre- and post-process utility programs and related scripts are also included in the FALL3D-7.1 distribution package. Several parameterizations can be chosen to describe eruption source geometry and physics, particle terminal settling velocity, eddy diffusivity tensor, and ash aggregation. For the meteorological variables FALL3D-7.0 uses an off-line strategy, i.e. variables are furnished by independent meteorological models or datasets and interpolated to the FALL3D-7.0 grid as NetCDF files. The FALL3D-7.1 model can be used to reproduce features of past eruptions, as a tool for short-term ash dispersal forecasting, and for volcanic fallout hazard assessment. Relevant changes have been introduced in FALL3D-7.1, including:

  • A unified source code for both serial and parallel versions (only the serial version was available for public distribution in previous releases);
  • The possibility of using forecasts/reanalysis meteorological data from several global/meso-scale meteorological models (not available for public distribution in previous releases);
  • Different parameterizations available for ash aggregation. For computational reasons, a preliminary Total Grain Size Distribution (TGSD) file (furnished either by the user or generated by the pre-process SETTGSD utility program) is modified in order to create the final "effective" granulometry file filename.grn which can include an aggregated class and a volatile species, treated as tracers;
  • An option describing the cloud spreading at the Neutral Buoyancy Level (NBL) for large eruptions using a semi-analytical gravity current model;
  • New parameterizations for resuspension of deposited volcanic ash by wind;
  • A parameterization to account for wet deposition;
  • Two new parameterizations to estimate cross-wind effects on Mass Eruption Eruption (MER);
  • A new multi-platform installation method that utilizes the configure command option. The program can be installed on different machines sharing the same filesystem or on a single machine that has different compilers.

Cite this work

Researchers should cite this work as follows:

  • Arnau Folch; Antonio Costa; Giovanni Macedonio (2016), "Fall3d-7.1," https://vhub.org/resources/3949.

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