Roland Draxler
Barbara Stunder
Glenn Rolph
Ariel Stein
Albion Taylor
Sonny Zinn
Chris Loughner
Alice Crawford

Version 5.2 - Last Revision: January 20221


Abstract The HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) Model installation, configuration, and operating procedures are reviewed. Examples are given for setting up the model for trajectory and concentration simulations, graphical displays, and creating publication quality illustrations. The model requires specially preformatted meteorological data. Programs that can be used to create the model's meteorological input data are described. The User's Guide has been restructured so that the section titles match the GUI help menu tabs. Although this guide is designed to support the PC and UNIX versions of the program, the executable of the on-line web version is identical. The only differences are the options available through the interface.


The HYsplit (HYbrid Single-Particle Lagrangian Integrated Trajectory) model is a complete system for computing trajectories complex dispersion and deposition simulations using either puff or particle approaches.2 It consists of a modular library structure with main programs for each primary application: trajectories and air concentrations.

Gridded meteorological data, on a latitude-longitude grid or one of three conformal (Polar, Lambert, Mercator) map projections, are required at regular time intervals. The input data are interpolated to an internal sub-grid centered to reduce memory requirements and increase computational speed. Calculations may be performed sequentially or concurrently on multiple meteorological grids, usually specified from fine to coarse resolution.

Air concentration calculations require the definition of the pollutant's emissions and physical characteristics (if deposition is required). When multiple pollutant species are defined, an emission would consist of one particle or puff associated with each pollutant type. Alternately, the mass associated with a single puff may contain several species. The latter approach is used for calculation of chemical transformations when all the species follow the same transport pathway. Some simple chemical transformation routines are provided with the standard model distribution.

The dispersion of a pollutant is calculated by assuming either a Gaussian or Top-Hat horizontal distribution within a puff or from the dispersal of a fixed number of particles. A single released puff will expand until its size exceeds the meteorological grid cell spacing and then it will split into several puffs. An alternate approach combines both puff and particle methods by assuming a puff distribution in the horizontal and particle dispersion in the vertical direction. The resulting calculation may be started with a single particle. As its horizontal distribution expands beyond the meteorological grid size, it will split into multiple particle-puffs, each with their respective fraction of the pollutant mass. In this way, the greater accuracy of the vertical dispersion parameterization of the particle model is combined with the advantage of having an expanding number of particles represent the pollutant distribution as the spatial coverage of the pollutant increases and therefore a single particle can represent increasingly lower concentrations.

Air concentrations are calculated at a specific grid point for puffs and as cell-average concentrations for particles. A concentration grid is defined by latitude-longitude intersections. Simultaneous multiple grids with different horizontal resolutions and temporal averaging periods can be defined for each simulation. Each pollutant species is summed independently on each grid.

The routine meteorological data fields required for the calculations may be obtained from existing archives or from forecast model outputs already formatted for input to HYSPLIT. In addition, several different pre-processor programs are provided to convert NOAA, NCAR (National Center for Atmospheric Research) re-analysis, or ECMWF (European Centre for Medium-range Weather Forecasts) model output fields to a format compatible for direct input to the model. The model's meteorological data structure is compressed and in "direct-access" format. Each time period within the data file contains an index record that includes grid definitions to locate the spatial domain, check-sums for each record to ensure data integrity, variable identification, and level information. These data files require no conversion between computing platforms.

The modeling system includes a Graphical User Interface (GUI) to set up a trajectory, air concentration, or deposition simulation. The post-processing part of the model package incorporates graphical programs to generate multi-color or black and white publication quality Postscript printer graphics.

A complete description of all the equations and model calculation methods for trajectories and air concentrations has been published3 and it is also available on-line. The on-line and the version included with the PC installation contains all the most recent corrections and updates.

Pre-Installation Preparation

There are two installation programs that can be downloaded. The trial version (HYSPLIT_win{32|64}U.exe ~ 70 Mb) available to anyone and a fully functional version (HYSPLIT_win{32|64}R.exe ~ 70 Mb) that requires a user registration through the web site. Both versions identical, except the trial version will not work with forecast meteorological data files. It is assumed that tcl/tk, web browser, and ImageMagick would have already been installed when the registered version is installed on top of the trial version.

The self-installing executable contains only HYSPLIT related programs. No additional software is required to run a simulation if the command line interface is sufficient. To enable the model's GUI, the computer should have Tcl/Tk script language installed. The most recent version can be obtained over the Internet. The installation of Tcl/Tk will result in the association of the .tcl suffix with the Wish executable and all Hysplit GUI scripts will then show the Tk icon. The HYSPLIT GUI has been tested with Tcl/Tk version 8.6.7.

The primary HYSPLIT graphical display programs convert the trajectory and concentration model output files to Postscript format or to Scalable Vector Graphics (SVG) format as HTML. The HYSPLIT GUI is configured to use SVG that can be viewed directly through web browser. The HYSPLIT code and GUI have been tested with Mozilla Firefox 78.12.0esr. Installation to different default drives, directories, or other versions might require editing the main GUI script's directory pointers (edit file: /guicode/hysplit.tcl or the directory entry in the Advanced-Configuration-Directories menu tab.

The third optional GUI feature is the ability to convert the SVG output file to a different graphical formats using ImageMagick. More information on this software can be found at The HYSPLIT code and GUI have been tested with ImageMagick 6.4. Installation to a different default drives or directories as suggested by the installation process may require editing the main GUI script's directory pointers. Although the setup script tests for the default language, it is possible that installation to non-English default windows operating systems might require additional editing of the directory pointers.

Windows Installation (all operating systems)

HYSPLIT installation to a computer running Windows is provided through a self-installing file. Executables are installed in various directories for trajectories, dispersion, display and manipulation of results, and the creation of input meteorological data files. The trajectory and dispersion model source code is not provided. However all the Fortran source code to create meteorological data files in a format that the model can read are provided in the /data2arl directory. Each subdirectory contains a @readme.txt file with more complete information about the contents of that directory.

During the installation you will be prompted as to the directory location. It is suggested you select a simple default location (such as C:/hysplit). The installation program installs all code and executables to your selected directory, and creates a shortcut on the desktop to /guicode/hysplit.tcl with the "Start In" directory as your selected default. You may have one of two versions of the installation program: HYSPLIT_win{32|64}{R|U}.exe. The suffixes R and U refer to the Registered or Unregistered versions. The two versions are almost identical, except that the unregistered version does not permit calculations with current forecast meteorological data.

HYSPLIT and all the related programs are available for either 32 bit or 64 bit operating systems. The 32 bit version can be installed on either OS, while the 64 bit programs can only be installed on a 64 bit OS. An Apple MAC version is also available (HYSPLIT_mac.dmg).

Installing on top of an old version will bring up a "Continue" or "Cancel" prompt. It is not possible to rename the installation directory at this stage. Rename your old installation prior to installing the new code if you wish to keep the original version.

The installation will contain several sub-directories, some of which are required for model execution, and some of which provide additional documentation and other information. For instance ...


If Tcl/Tk does not exist on your system or there are other problems with the GUI interface, it is very easy to run the sample cases directly in the /working directory by running the batch file "run_{model}.bat" If the sample simulation works well, then it is only necessary to manually edit the CONTROL file to try out different simulation variations. The CONTROL file options are explained in more detail in the individual Trajectory and Concentration Setup sections.

In general, premature termination during the model initialization phase will result in messages to standard output. However after the model has started, fatal, diagnostic, and progress notification messages are written to a file called Message. If the model output is not what you expected, first check the Control file to determine if the input setup is what is desired, then check the Message file for indication of abnormal performance. These files are always written to the model's startup directory - /Hysplit if the model is run from the GUI. At times error messages may be lost in the display buffer after premature termination. In this case the model should be rerun from the command line window for proper display of all standard output messages. The "Advanced" menu contains a the View MESSAGES tab that displays the last MESSAGE file for viewing. Other features of the advanced menu are used to modify the model's configuration file and are explained in more detail in that section. Modifications to these parameters require a complete understanding of the model's design and operation.