# Exercise #5

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• Problem #1 - The computational error tutorial (section 4.5) showed only minor differences when the initial trajectory height was 600 m compared to the calculation from 10 m, which showed a much larger difference. Repeat the calculation using an initial height of 10 m.

• Hint - Edit and then run traj_error.bat or traj_error.sh.

• Solution - Computational result. Can you explain how terrain might have caused the trajectory differences?

• Problem #2 - Section 5.4 showed you how to create multiple trajectories in time in a single output file. Although the GUI option has not yet been discussed, see if you can figure out how to automatically create a new mid-boundary layer trajectory each hour for 24 h starting at 1700 UTC, but each one written to its own output file.

• Hint - Retrieve traj_fwrd_control.txt and edit the trajectory setup menu to define a simple output file name with just one letter: T. Then open the Special Runs / Daily menu and set the start interval and duration to one followed by execute script to obtain 24 trajectories, one per output file.

• Solution - Open the command line prompt and go to the HYSPLIT working directory and create a file of trajectory file names by entering the command dir /b T8309* >INFILE (use ls for UNIX or MacOS). Then open the trajectory plotting menu and enter +INFILE into the input endpoints field to obtain the multi-trajectory graphic.

• Problem #3 - In exercise #4 problem #3 we found that all the trajectories using instantaneous winds were similar, but the one using time-averaged winds was considerably different toward the end. Can you determine which caused the greatest difference, the time-averaging of the horizontal or the vertical winds?

• Hint - Turn off the vertical motion (isosigma option) and compare the trajectories using the wrf27uw and wrf27mc data files.

• Solution - The result shows that in this particular case, time-averaging of the vertical motion caused the most difference in the trajectory. However, this may not be the case for other locations or meteorological situations.