Time of arrival graphic (isochron) shows the time after the start of the simulation that the concentration exceeds the given threshold concentration at each concentration grid cell. The default contour interval (-1) uses the concentration averaging period. Otherwise, the time difference field should be set to hours. A text label with release information may be printed below the threshold through the LABELS.CFG file.
The GUI and the command line options are similar with the command line syntax as follows: USAGE: isochron -[options(default)]
In the 144 hour duration example simulation shown below, the concentration field was output every six hours, the contour interval was set to 12 hours, and the threshold to 0.1E-15 . The one hour duration release took about 72 h to reach Hudson's Bay and about 144 h to reach into the Atlantic off the east coast of the U.S.