Hands-On Exercise #9 ©

Exercise #9
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Problem #1 - The 914 m AGL flight data file contained results from a sampling pass about 2 hours earlier (around 0100 on 26 September) than the one used in the previous examples. Would the base case simulation result be similar using these sampling data?

Hint - Retrieve conc_case_control.txt and conc_case_setup.txt and reconfigure the simulation for a sampling time between 0100-0200. Create your own measured data file with the appropriate start times or use the one provided: data_case0.txt.

Solution - How are these earlier aircraft results different from the original example collected two hours later?

Problem #2 - Again retrieve conc_case_control.txt and conc_case_setup.txt to run the original example but this time configure the simulation to determine the concentration profile at the location of measurement maximum (rounding to 0.05 degrees: 41.1, -82.5).

Solution - Use the concentration display to show the contours at each level. Comparing the results for the two lowest layers (250 m and 500 m MSL), why does the lowest layer show a much smaller plume? Another way to extract the concentration profile is to use the utility convert to ASCII. Open the output file (hysplit2.bin.txt) to find the grid point nearest to the maximum measured concentration The profile shows that the maximum occurred between 500-750 m MSL. The profile could also be imported into a spreadsheet for display.

Problem #3 - Although many of the different turbulence methods showed similar results at the aircraft sampling level, how were the other levels affected? Try comparing the calculation using the default flux method with the calculation using TKE.

Hint - Rather than adding multiple output levels for concentration, compare the vertical mass profiles in the MESSAGE file. These are only output every 6 h and to see the profile nearest in time to the aircraft sampling pass, you need to increase the simulation time from 11 to 12 h.

Solution - The aircraft pass was at 914 m MSL and the MESSAGE file output is m AGL. The terrain height at the peak concentration point along the aircraft pass was determined to be 288 m MSL (use the profile program) and therefore the height of the aircraft pass at the peak point would be 626 m AGL. Comparing the MESSAGE file profiles after 12 h for the flux calculation with the profile from the TKE calculation, shows that the higher concentrations seen along the pass (570-730 m AGL) are consistent with the greater mass at those levels (570-1330 m AGL), compensated by generally slightly lower mass at the other levels. Because of the short-duration release and short travel times, the tracer plume is constrained to a smaller region, and thereby permitting conclusions to be drawn from the diagnostic information contained in the MESSAGE file.