The Lagrangian particle dispersion model FLEXPART

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The Lagrangian particle dispersionmodel FLEXPART

• Jimmy LECLAIR DE BELLEVUE
• Presentation to UKZN training
• session - 09 Nov 2006
• 3-D visualization of an intrusion of
  stratospheric
• air into the troposphere, resulting from a
• FLEXPART simulation.
• The domain shown covers Europe, and the
• uppermost level is at 13 km

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Content

• References
• Introduction
• What is good in FLEXPART ?
• System requirements versions
• Summary of the available versions
• Setup
• Use
• Important aspects of the physics
• Case studies of stratospheric to tropospheric
  exchanges Examples
• Take-Home message

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References

• http//zardoz.nilu.no/andreas/flextraflexpart.ht
  ml
• Descriptions of FLEXPART in the scientific
  literature are
• Stohl, A., M. Hittenberger, and G. Wotawa (1998)
  Validation of the Lagrangian particle dispersion
  model FLEXPART against large scale tracer
  experiments. Atmos. Environ. 32, 4245-4264.
• Stohl, A., and D. J. Thomson (1999) A density
  correction for Lagrangian particle dispersion
  models. Bound.-Layer Met. 90, 155-167.
• Stohl, A., C. Forster, A. Frank, P. Seibert, and
  G. Wotawa (2005) Technical Note The Lagrangian
  particle dispersion model FLEXPART version 6.2.
  Atmos. Chem. Phys. 5, 2461-2474.

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Introduction

• FLEXPART is an atmospheric trajectory and a
  particle dispersion model, respectively, that are
  used by a growing user community.
• A recent user survey resulted in 34 groups from
  17 countries who have confirmed to actively use
  one of the models for a variety of research
  purposes.
• Applications of the models cover topics like
  transport of radionuclides after nuclear
  accidents, pollution transport, greenhouse gas
  cycles, stratosphere-troposphere exchange, water
  cycle research, and others.
• Development supervised by Andreas Stohl and
  mainly by people from
• Norwegian Institute of Air Research, Kjeller,
  Norway
• Institute of Meteorology, University of Natural
  Resources and Applied Life Sciences, Vienna,
  Austria
• Preparatory Commission for the Comprehensive
  Nuclear Test Ban Treaty Organization, Vienna,
  Austria
• FLEXPART is being developed continuously !

http//zardoz.nilu.no/andreas/
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Introduction

• Lagrangian particle models compute trajectories
  of a large number of so-called particles (not
  necessarily representing real particles, but
  infinitesimally small air parcels) to describe
  the transport and diffusion of tracers in the
  atmosphere.
• The main advantage of Lagrangian models is that,
  unlike in Eulerian models, there is no numerical
  diffusion.
• FLEXPART is a Lagrangian particle dispersion
  model that simulates the long-range and mesoscale
  transport, diffusion, dry and wet deposition, and
  radioactive decay of tracers released from point,
  line, area or volume sources.
• FLEXPART can be used forward in time to simulate
  the dispersion of tracers from their sources, or
  backward in time to determine potential source
  contributions for given receptors.

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What is good in FLEXPART ?

• FLEXPART was evaluated using data from three
  large-scale tracer experiments, namely the
• Cross-Appalachian Tracer Experiment (CAPTEX),
• Across North America Tracer Experiment (ANATEX)
• European Tracer Experiment (ETEX),
• comprising a total of 40 releases.
• The results of this validation study are
  described in Stohl et al. (1998), but in summary
  one can say that FLEXPART seems to belong to the
  better dispersion models currently available.
• This is also supported by the ATMES-II model
  intercomparison study, where FLEXPART scored
  among the best models.
• It requires only a short computation time, has a
  finer spatial resolution and does not suffer
  numerical diffusion compared to chemistry
  transport models (CTMs).
• It is a compromise between simple trajectory
  calculations and complex CTMs that makes best use
  of available computer hardware.
• The model is freeware and can be downloaded

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System requirements versions

• FLEXPART, written in FORTRAN 77, is largely
  platform independent. It currently runs on SUN,
  SGI, HP, Compaq Alpha and LINUX workstations.
• (also on IBM, done in Reunion Island
  University)
• FLEXPART can be driven with meteorological input
  data from a variety of global and regional
  models, most commonly from the European Centre
  for Medium Range Weather Forecasts (ECMWF).
• It runs where a Fortran 77 compiler and a GRIB
  decoding software to read ECMWF input data.
• The memory requirements depend on the spatial
  domain of your input fields and the number of
  particles you want to use.
• The ECMWF version of the model is considered as
  the reference version, but a new GFS version of
  FLEXPART is available (porting of the ECMWF
  version to use GFS data).

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Summary of the available versions

• FLEXPART V6.2 (based on ECMWF input data)
• FLEXPART V6.4 for GFS (Contact Caroline Forster
  caroline.forster_at_dlr.de)
• On 24 April 2002 the NCEP AVN model was renamed
  to the GFS (Global Forecast System)
• GFS Products http//www.nco.ncep.noaa.gov/pmb/pr
  oducts/gfs/
• FLEXPART V3.1 for MM5
• FLEXPART for WRF (Contact Jerome Fast
  Jerome.Fast_at_pnl.gov)
• The Weather Research and Forecasting (WRF) Model
  is a next-generation mesocale numerical weather
  prediction system designed to serve both
  operational forecasting and atmospheric research
  needs.
• The effort to develop WRF has been a
  collaborative partnership, principally among the
  National Center for Atmospheric Research (NCAR),
  the National Oceanic and Atmospheric
  Administration (the National Centers for
  Environmental Prediction (NCEP) and the Forecast
  Systems Laboratory (FSL), the Air Force Weather
  Agency (AFWA), the Naval Research Laboratory,
  Oklahoma University, and the Federal Aviation
  Administration (FAA).
• WRF homepage http//www.wrf-model.org/index.php
• Routines for the retrieval of FLEXPART input data
  from ECMWF
• Tools to analyze the output NCAR Graphics
  programs and statistical programs available

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Setup of FLEXPART
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The pathnames file

• A file pathnames must exist in the directory
  where FLEXPART is started. It states the
  pathnames of input and output files
• /home/as/FLEXPART50/options/
• /volc/as/contrace/modelresults/forward/
• /volc/windcontrace/
• /volc/windcontrace/AVAILABLE
• /volc/nested/
• /volc/nested/AVAILABLE
• Line 1 path where control files "COMMAND" and
  "RELEASES" are available
• Line 2 name of directory where output files are
  generated
• Line 3 path where meteorological fields are
  available (mother grid)
• Line 4 full filename of "AVAILABLE"-file (mother
  grid)
• Subsequent lines
• Line 2n3 path where meteorological fields are
  available (nested grid n)
• Line 2n4 full filename of "AVAILABLE"-file
  (nested grid n)

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The file Includepar

• The file includepar contains all relevant
  FLEXPART parameter settings, both physical
  constants and maximum field dimensions.
• As the memory required by FLEXPART is determined
  by the various field dimensions, it is
  recommended that they are adjusted to actual
  needs before compilation.
• To avoid  segmentation fault , change the
  variables size
• maxpart(2000)
• maxpoint (1)
• maxrand(2000)
• Compilation make f makefile

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Use of FLEXPART
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The AVAILABLE file

• The directory where the meteorological input data
  are stored, here called windfields
  (/volc/windcontrace/ in the above example
  pathnames file), contains grib-code files
  containing the ECMWF data. All meteorological
  fields must have the same structure, i.e. the
  same computational domain and the same
  resolution. An example listing of this directory
  is given below.
• The file names of the grib-code files and their
  validation dates and times (in UTC) must be
  listed in the file AVAILABLE. While it is
  practical to have this file reside in the same
  directory as the wind fields, this is no
  necessity and it can also be located elsewhere,
  as its file name is also given in the pathnames
  file.
• DATE TIME FILENAME SPECIFICATIONS
• YYYYMMDD HHMISS
• ________ ______ __________ __________
• 20011028 000000 EN01102800 ON DISC
• 20011028 030000 EN01102803 ON DISC
• 20011028 060000 EN01102806 ON DISC
• 20011028 090000 EN01102809 ON DISC
• 20011028 120000 EN01102812 ON DISC

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Files in directory options

• The files in directory options are used to
  specify the model run.
• Very important are
• COMMAND
• RELEASES
• OUTGRID
• File COMMAND
• The most important file is the COMMAND file which
  specifies (1) the simulation direction (either
  forward or backward), (2) the start and (3) the
  end time of the simulation, (4) the frequency Tc
  of the model output, (5) the averaging time Tc of
  model output, etc

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Files in directory options

• File RELEASES
• RELEASES defines the release specifications
• The beginning and the ending time of the release,
  
• Geographical coordinates of the lower left and
  upper right corners of the release location,
• type of vertical coordinate (above ground level,
  or above sea level),
• lower level and upper level of source box,
• the number of particles to be used
• The particles are released from random locations
  within a four-dimensional box extending from the
  lower to the upper level above a rectangle (on a
  lat/lon grid) defined by the geographical
  coordinates, and between the releases start and
  end.

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Files in directory options

• The file OUTGRID specifies the output grid,
  Change if necessary
• EXECUTION OF FLEXPART
• ./FLEXPART
• rather quick, a few dizaines of particles during
  five days lt 10 minutes

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Important aspects of the physics in FLEXPART

• Mesoscale velocity fluctuations
• Mesoscale motions are neither resolved by the
  ECMWF data nor covered by the turbulence
• parameterization.
• This unresolved spectral interval needs to be
  taken into account at least in an approximate
  way, since mesoscale motions can significantly
  accelerate the growth of a dispersing plume
  (Gupta et al., 1997).
• For this, a similar method as Maryon (1998),
  namely to solve an independent Langevin equation
  for the mesoscale wind velocity fluctuations
  (meandering in Maryons terms).
• This empirical approach does not describe actual
  mesoscale phenomena, but it is similar to the
  ensemble methods used to assess trajectory
  accuracy (Kahl , 1996 Baumann and Stohl, 1997
  Stohl, 1998).

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Important aspects of the physics in FLEXPART

• Moist Convection
• An important transport mechanism are the updrafts
  in convective clouds.
• They occur in conjunction with downdrafts within
  the clouds and compensating subsidence in the
  cloudfree surroundings.
• These convective transports are grid-scale in the
  vertical, but sub-grid scale in the horizontal,
  and are not represented by the ECMWF vertical
  velocity.
• To represent convective transport in a particle
  dispersion model, it is necessary to redistribute
• particles in the entire vertical column.
• For FLEXPART the convective parameterization
  scheme chosen is from Emanuel and
  Zivkovic-Rothman (1999), as it relies on the
  gridscale temperature and humidity fields and
  calculates a displacement matrix providing the
  necessary mass flux information for the particle
  redistribution.
• The convective parameterization is switched on
  using lconvection in file COMMAND.
• Its computation time scales to the square of the
  number of vertical model levels and may account
  for up to 70 of FLEXPARTs computation time
  using current 60-level ECMWF data.

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Important aspects of the physics in FLEXPART

• Clustered plume trajectories
• In a recent paper, Stohl et al. (2002) proposed a
  method to condense the complex and large
• FLEXPART output using a cluster analysis (Dorling
  et al., 1992).
• The idea behind this is to cluster, at every
  output time, the positions of all particles
  originating from a release point, and write out
  only clustered particle positions.
• This option can be activated by setting iout to 4
  or 5 in file COMMAND.
• The number of clusters can be set with the
  parameter ncluster in file includepar.
• Output
• Condensed particle output using the clustering
  algorithm is written to the formatted file
  trajectories.txt.
• Information on the release points (coordinates,
  release start and end, number of particles) is
  written by subroutine openouttraj.f to the
  beginning of file trajectories.txt.
• Subsequently, plumetraj.f writes out a time
  sequence of the clustering results for each
  release point release point number, time in
  seconds elapsed since the middle of the release
  interval, plume centroid position coordinates,
  and then for each cluster the cluster centroid
  position, the fraction of particles belonging to
  the cluster, and the root-mean-square distance of
  cluster member particles from the cluster
  centroid.

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Case studies of tratospheric to tropospheric
exchanges Examples
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IRENE
Clustered plume trajectories
REUNION
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Not clustered plume trajectories
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Take-home message

• Thanks for your attention !
• You will read the following later
• Access and use of FLEXPART shall impose the
  following obligations on the user.
• The user is granted the right, without any fee or
  cost, to use, copy, modify, alter, enhance and
  distribute FLEXPART, and any derivative works
  thereof, and its supporting documentation for any
  purpose whatsoever, except commercial sales,
  provided that this entire notice appears in all
  copies of the software, derivative works and
  supporting documentation.
• This software is provided by the University of
  Munich "as is" and any express or implied
  warranties, including but not limited to, the
  implied warranties of merchantability and fitness
  for a particular purpose are disclaimed. In no
  event shall the University of Munich be liable
  for any special, indirect or consequential
  damages or any damages whatsoever, including but
  not limited to claims associated with the loss of
  data or profits, which may result from an action
  in contract, negligence or other tortious claim
  that arises out of or in connection with the
  access, use or performance of FLEXPART.

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Schematic of a lagrangian model