Example 7 Meteorological Analysis along a Trajectory

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Example 7Meteorological Analysis along a
Trajectory

• Configure a trajectory run to plot the model
  terrain height along the trajectory path.
• Change the vertical motion method from Model
  Vertical Velocity to Isentropic to view
  differences.

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Run a forward trajectory with NAMF12 forecast
data from the Workshop archive.
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Choose Source Location
Enter a starting location at 39.92N and 105.12W
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Model Runtime Options
Total run time 84 hours
Starting height 1500 m AGL
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Display Options
Vertical plot height units Pressure
Check Terrain Height to plot along trajectory.
Note this will not plot the terrain heights, but
will calculate them.
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Submit the job and view the results
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The resulting trajectory proceeds to the
southeast into central Texas, descending from 700
hPa to nearly 950 hPa.
Now click on Modify the trajectory plot without
rerunning the model from the results page.
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Vertical plot height units Above model ground
level
Click Request plot.
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Submit the graphics job and view the results
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The same trajectory is plotted, and since the
terrain height along the trajectory was already
saved, it is plotted below the trajectory (this
can also be done by rerunning the model and
clicking Yes to plot the meteorological data
along the trajectory). The trajectory actually
follows the terrain for the most part, so care
must be exercised when interpreting the up or
down movement of trajectories wrt terrain.
The terrian heights (MAGL) along the trajectory
can be viewed as the right-most column of the
trajectory endpoints file.
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Use the option to rerun the job
A recently added option, allows a user to rerun a
model case from the results page without having
to re-enter all the inputs previously entered.
Click on Rerun the model with user entered
defaults from the results page.
Check Plot meteorological field along
trajectory.
Uncheck Terrain Height and check Mixed Layer
Depth.
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Submit the job and view the results
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This plot shows the mixed layer depth along the
trajectory varied from 250 m to 687 m. (The
HYSPLIT trajectory model sets the minimum mixing
height to 250 m.)
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Review Vertical Motion Options discussion before
proceeding.
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Use the option to rerun the job
Now we will rerun the model using the Isentropic
vertical motion option to demonstrate the
differences observed between model vertical
motion and Isentropic motion.
Vertical Motion Isentropic
Vertical plot height units Theta
Click on Rerun the model with user entered
defaults from the results page.
Also, Uncheck Plot meteorological field along
trajectory and uncheck Mixed Layer Depth.
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Submit the job and view the results
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Shown below left is the trajectory from Example 7
using the NAM 12 km vertical velocity fields.  To
the right is the same trajectory computed using
the isentropic flow assumption and choosing the
Theta vertical coordinate option. This graphic
shows that the potential temperature varied by
only about 1 degree, however by assuming
adiabatic flow conditions the second trajectory
ended in northeastern Louisiana after 84 hours
instead of north central Texas. The validity of
the adiabatic flow assumption would need to be
assessed for this case (no precipitation, cloud,
etc).
Isentropic
Model Vertical Velocity