Trajectory Model Configuration

The Trajectory Setup menu has several options that control the computation. Usually they should be left at their default values.  For instance, computations should use the vertical motion field (Data) contained within the data file.  Only under special situations, such as the previous example, should other methods be selected.  Some of these options will be explored in more detail later.  The Top of the model (m agl) is the height above which the meteorological data are not processed.  For calculations within the troposphere, 10 km is a good top.  Trajectories are terminated when they reach this height.  Processing fewer levels reduces computational times. A starting location can be entered directly from the Setup starting locations menu or a position may be chosen from a predefined List.  This list is user editable and named plants.txt.

One key feature for any simulation is selecting the best meteorological data files.  In the current compiled version up to 12 files may be defined simultaneously. When multiple files are defined, at each integration step, the model finds the finest spatial resolution file at the location and time of the trajectory end-point.  For the next example, select a height of 2.5 km in Maine (46N, 68W) and also select isobaric as the vertical motion method. Set the Total run time to 84 hours and select both the NAMF12 and GFSFLL meteorological data files. Execution of the CONTROL file for this case results in a trajectory that goes northeast using the NAM 12 km forecast file until running off the NAM domain. The model then uses the GFS for the remainder of the calculation.

The meteorological file indentifier is written with each end-point position in the second column of the ASCII trajectory tdump output file. The diagnostic MESSAGE file also provides additional detail about the calculation.  In this example the switch from NAM to GFS occurs at 0900 GMT on December 20, 2005, causing the 0900 and 1200 GMT data to be reloaded.