The HYSPLIT package for computing trajectories and plume dispersion consists of a series of command line based executable programs that are integrated through a number of different scripts that create the required input files and run the programs. These scripts are all invoked through a Graphical User Interface (GUI). An overview of the GUI follows:
- Once the installation is complete, that is the HYSPLIT code and all the auxiliary software are installed, then click the desktop icon Run Hysplit and a startup window will be shown. Select the menu button to proceed.
- The main menu consists of four main tabs: meteorology, trajectory, concentration, and advanced. There are multiple sub-tabs under each main tab which are all shown in the open position in this document for illustration. Individual sub-menus will be discussed as needed.
- The meteorology tab provides for different ways to access meteorological data files and load them into the local computer to perform trajectory or dispersion calculations. For the purposes of this tutorial, all required meteorological data files are provided with the HYSPLIT installation or in the directories of the tutorial CD-ROM.
- The trajectory tab opens access to sub-menus to setup the trajectory simulation, run the calculation, and then display the results. A trajectory is just the integration of the position vector through a wind field that varies in space and time. The point is assumed to be passively transported by the wind.
- The concentration tab has similar sub-menus to the trajectory calculation. The primary difference between the two is that the trajectory calculation only follows one point transported by the mean wind, while the concentration calculation may follow thousands of trajectories at the same time, the motion of each being composed of a mean (trajectory) and turbulent (dispersive) component. In addition, each "particle" trajectory associated with the concentration calculation has some mass assigned to it which means that the trajectory density can be used to compute an air concentration.
- The advanced tab is used to set additional model parameters that can be used to provide further control or customization to either the trajectory or concentration calculation. The information is written to a namelist file, always called SETUP.CFG. A namelist file contains the value of various program variables defined by their internal code name. Some other miscellaneous features can also be found under this tab.
- The basic model operation involves three steps. First Setup Run configures the simulation details and saves the information to a file called default_traj or default_conc. Second, when Model Run is invoked, the default_???? file is copied to a file named CONTROL which is then read by the model executable. Third, the Display menu will call a program to read the model output file and will create a Postscript graphics file. These are all written to the working directory. In subsequent tutorial pages these menus will be explored in considerably more detail.
- GUI Hints
- Avoid having multiple windows open at the same time.
- Close a window when finished with the Close button rather than the red X in the upper right corner.
- If a GUI error message appears, first close the entire GUI and then restart. If that does not solve the problem, press the reset button to configure the test case, and then rebuild your simulation step-by-step, testing the model with each change.
- In some cases after running multiple different simulations in sequence without closing the GUI, certain menus when first opened may populate with missing or unexpected initial values carried over from previous simulations. In this case, closing and restarting the GUI should also solve the problem.
The HYSPLIT input file and program structure supported by the GUI are summarized by a simplified flowchart.