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What is FLEXPART?

FLEXPART is a Lagrangian particle dispersion model developed and used by a large international scientific community. It can be driven by meteorological input data from a variety of global and regional models including ECMWF analyses and forecasts.

The home of the software is https://www.flexpart.eu/.

How to use FLEXPART with Metview?

VAPOR has its own internal data model and NWP data has to be converted into the VAPOR format.  There are a set of VAPOR command line tools that can convert NetCDF input data into this format but there is no such tool available for GRIB.

Metview's VAPOR Prepare icon helps to overcome this difficulty and allows converting GRIB data into the VAPOR format.

Once the conversion has been completed the VAPOR Prepare icon can be used to start up VAPOR to provide interactive 3D visualisation for the data. The snapshots below show how ECMWF data is actually displayed in VAPOR.

FLEXTRA can compute both forward and background trajectories using various trajectory types such as: three-dimensional, model level, mixing layer, isobaric and isentropic trajectories. Trajectory computations can be carried out in the three different modes. These are as follows:

  1. In NORMAL mode, a group of trajectories is specified starting from the same point but at different times. Several starting points (thus several groups of trajectories) can be defined for a single FLEXTRA run.
  2. In CET mode, trajectories are generated starting from the points of a user-defined uniform grid in a three-dimensional domain.
  3. In FLIGHT mode, both the starting location and starting time for each trajectory can be set individually. This mode is useful to calculate e.g. trajectories along the flight track of an aircraft.

 

FLEXTRA is a free software system released under the GNU General Public License V3.0. The joint homepage of FLEXTRA and FLEXPART (a Lagrangian particle dispersion model) is hosted by the Norwegian Institute for Air Research (NILU) and available at the following address:

http://transport.nilu.no/flexpart

This website contains a link to the latest available FLEXTRA documentation:

http://zardoz.nilu.no/~andreas/flextra/flextra3.html

 

Please note that FLEXTRA is not an ECMWF development. FLEXTRA is not distributed with Metview, but it has to be downloaded from the web site specified above and installed separately. It is installed at ECMWF though.

About the Metview interface

Metview provides a high level interface to prepare input data for FLEXTRA, run FLEXTRA and visualise the resulting output files. The interface was developed and tested with version 5.0 of FLEXTRA, which is using GRIB API to handle GRIB2 fields.

The input file generation and visualisation do not require the existence of a FLEXTRA executable. However, FLEXTRA itself can be only run if an executable is present. The path to the FLEXTRA executable can be specified for Metview at installation time by setting the --with-flextra switch for configure. However, this path can be overridden at Metview start-up via the MV_FLEXTRA_EXE environment variable.

FLEXTRA is controlled through a set of parameter files which are all generated automatically by Metview in the background. The only exception is file AVAILABLE which can optionally be provided by the users (see Part 3 for details).

Further details

There is a tutorial available on the use of VAPOR with Metview. It explains both the data preparation steps and the basics of the visualisation.

Details about setting up the Metview FLEXPART interface outside ECMWF can be accessed here.
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