This is the direction of the trajectory calculation. Note that you must change the default starting time when computing FORECAST backward trajectories because the default time is the start of the meteorological forecast, and thus the model cannot calculate backward prior to the initial forecast time.
This is the type of vertical motion method the model should use in its calculation. For most simulations, choose the default "Model vertical velocity" that will use the vertical velocity field from the meteorological data. Other options include Isobaric (constant pressure surface) and Isentropic (constant potential temperature surface).
Specify the duration of the calculation in hours. The default number in the case of forecast trajectories corresponds to the maximum length of the forecast dataset. A maximum of 315 hours can be specified for archive datasets on the web, 48 hours for forecast ensemble trajectories, and 84 hours for balloon optimization trajectories. If the model runs out of meteorological data it will terminate automatically.
Specify how often (every X hours) a new trajectory is started from the source location. At this time, only a total of 24 trajectories may be started and the maximum trajectory duration is 72 hours for each trajectory. If multiple levels are specified, only the first trajectory will be processed.
Up to 3 simultaneous trajectories can be calculated at multiple levels. Enter the heights with the lowest height in input box 1. Then check the box for either meters above model ground level or meters above mean sea-level. If entered as meters above mean sea-level, the model will convert them to meters above model ground level during the trajectory calculation. If they are below the model ground level, they will be assigned a height of zero meters above model ground level.
NOTE: Please be aware of the following issue: when running more than one trajectory (multiple levels) in the same run, the time step of the model may change based on where the other trajectories are located. The time step is set by the fastest trajectory the last hour, when there are more than one trajectory, this could result in a different time step for any one trajectory than if it were run by itself. When a trajectory is sensitive to the time step, this means that the spatial gradients in the velocity field are too strong and there should be less confidence given to the accuracy of any one trajectory. If this is an issue for your work, run only one trajectory at a time.
The GIS Shapefiles option will save all the contours for each plot first as lat/lon positions in an ESRI ArcInfo/ArcView GENERATE format ASCII file and then as shapefiles that can be imported into the ArcInfo/ArcView GIS program (and should also be a simple task to import them into any other GIS program). The Google Earth/Maps option will save the contours in KML format that the Google Earth pnd Google Maps programs can read and display.
Choose the resolution (size) of the final graphic images in dots-per-inch (dpi), which is what is calculated for creating the Postscript graphics. The larger the dpi, the larger the GIF image and the clearer the lines/text, but at the expense of larger files and a longer download time.
The zoom factor allows the user to "zoom in" on the trajectories with 0 being the least zoomed and 100 being the most zoomed in on the trajectories.
The output graphic can be plotted on a polar stereographic, lambert conformal, or mercator projection. The Default will depend on the source location latitude.
The final graphic has the trajectories plotting in the x-y plane and the z-t plane. The z-t plane shows the trajectories in the vertical (z) with time (t). You can choose the z height units in pressure coordinates, height in meters above model ground level, or theta if Isentropic trajectories were created.
The trajectories can be labelled every x hours with a symbol. Choices are no labels, or every 6, 12, or 24 hours.
This option will plot distance circles around the source location at the interval specified. The Auto option will draw 4 circles around the source with a "best fit" interval. Adding circles will override the zoom option settings to some extent.
This option will overlay U.S. county borders onto the plot. NOTE: Some of the county borders are not complete where incorporated cities are within the county (due to a software error in the conversion program).
HYSPLIT creates Postscript graphics when the plots are created, which are then converted to GIF files. However, the user may save the Postscript graphic for display or download if desired. The Postscript file is vector-oriented so that it is scalable and makes a clearer image when printed, however the filesize is much larger (can be several megabytes) than a GIF image, a consideration if access is via a slow connection. A Postscript viewer is also necessary to view a Postscript file.
Diagnostic meteorological varaiables can be output in the trajectory endpoint file (tdump). These variables are the values used or computed by HYSPLIT at each trajectory endpoint location. The choices are: terrain height (m), potential temperature (K), ambient temperature (K), rainfall (mm per hour), mixed layer depth (m), relative humidity and downward solar radiation flux (W/m**2). These variables can be useful in diagnosing the weather and mixing potential along the trajectory. NOTE: If you choose Meters AGL as the vertical plot height unit above (the default) and choose terrain height here, the vertical plot height unit will be changed to Meters ASL and the terrain height will be plotted in black on the vertical cross-section section of the trajectory output plot.
