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Hybrid Single-Particle Lagrangian Integrated Trajectory —


The HYSPLIT model is a complete system for computing simple air parcel trajectories to complex dispersion and deposition simulations. The intial development was a result of a joint effort between NOAA and Australia's Bureau of Meteorology. Recent upgrades include enhancements provided by a number of different contributors. Some new features include improved advection algorithms, updated stability and dispersion equations, continued improvements to the graphical user interface, and the option to include modules for chemical transformations. Without the additional dispersion modules, Hysplit computes the advection of a single pollutant particle, or simply its trajectory.

Example of a specialized HYSPLIT model 
				simulation of radioactive Cesium particles from the Japanese Daiichi Nuclear Power Station

The dispersion of a pollutant is calculated by assuming either puff or particle dispersion. In the puff model, puffs expand until they exceed the size of the meteorological grid cell (either horizontally or vertically) and then split into several new puffs, each with it's share of the pollutant mass. In the particle model, a fixed number of particles are advected about the model domain by the mean wind field and spread by a turbulent component. The model's default configuration assumes a 3-dimensional particle distribution (horizontal and vertical).

The model can be run interactively on the Web through the READY system on our site or the code executable and meteorological data can be downloaded to a Windows or Mac PC. The web version has been configured with some limitations to avoid computational saturation of our web server. The registered PC version is complete with no computational restrictions, except that user's must obtain their own meteorological data files. The unregistered version is identical to the registered version except that plume concentrations cannot be calculated with with forecast meteorology data files. The trajectory-only model has no restrictions and forecast or archive trajectories may be computed with either version.

Model Features


  • Single or multiple (space or time) simultaneous trajectories
  • Optional grid of initial starting locations
  • Computations forward or backward in time
  • Default vertical motion using omega field
  • Other motion options: isentropic, isosigma, isobaric, isopycnic
  • Trajectory ensemble option using meteorological variations
  • Output of meteorological variables along a trajectory
  • Integrated trajectory clustering option

Air Concentrations

  • 3D particle dispersion or splitting puffs (top-hat or Gaussian)
  • Instantaneous or continuous emissions, point or area sources
  • Multiple resolution concentration output grids
  • Fixed concentration grid or dynamic sampling
  • Wet and dry deposition, radioactive decay, and resuspension
  • Emission of multiple simultaneous pollutant species
  • Automated source-receptor matrix computation
  • Ensemble dispersion based on variations in meteorology, turbulence, or physics
  • Concentration probability output for multiple simulations
  • Integrated dust-storm emission algrorithm
  • Define rate constants to convert one species to another
  • Mass can be transferred to a Eulerian module for global-scale simulations


  • Model can run with multiple nested input data grids
  • Links to ARL and NWS meteorological data server
  • Access to forecasts and archives including NCAR/NCEP reanalysis
  • Additional software to convert MM5, RAMS, COAMPS, WRF, and other data
  • Utility programs to display and manipulate meteorological data

Common Features

  • Tcl/Tk GUI with integrated html compatible help
  • Viewer to display TOMS aerosol index with model particle positions
  • Model restart from particle position files for plume initialization
  • Model graphics displayed as Postscript files
  • Converters to many other formats: GIF, GrADS, ArcView, Vis5D

Further Information

Modified: April 8, 2014
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