Differences between results at different output resolutions and discrepancy between ascii values and corresp. contouring

Post questions, comments and links to research (research papers, web sites, etc) involving HYSPLIT and radiological nuclides. This section is also to facilitate collaborations between researchers involved in radiological nuclide transport and dispersion.
Post Reply
fppiguet
Posts: 8
Joined: June 18th, 2018, 9:25 am
Registered HYSPLIT User: Yes

Differences between results at different output resolutions and discrepancy between ascii values and corresp. contouring

Post by fppiguet »

Hello,
We compute radioactive dispersion out various nuclear plants. In doing this we fell on some unexplained behavior 1) on the dependency of the output resolution 2) on the difference between the numerical values generated by con2asc and the isolines generated by concplot.
For both aspects we ran Hysplit using meteorological fields with a resolution of 0.25° (gfs0p25). Keeping all the rest the same we varied the output resolution by using (0.05 0.05), (0.1 0.1) and (0.2 0.2).
Aspect 1:
If we superimpose the resolution 0.05 and 0.2 we see that the shapes of the higher thresholds are quite different. In particular, the surface of the red surface (contour level 3.9E+10 Bq-s/m3) is quite different. Would one estimate the amount of people touched by this amount of radioactivity the result would be very different.
00_image_1.png
In another contribution to the forum we saw that it would be wise to choose and output resolution which is not too different from the meteorological resolution, meaning that the smaller red area (corresponding to the resolution 0.2) would give the better representation of the real concentration of radioactivity in the air. Is that correct?
Aspect 2
Starting from the same cdump file, we extracted the ascii values by using the routine con2asc and generated a kml file using the concplot utility. It turns out that the results are quite different regardless of the resolution. The figure illustrates the difference:
00_image_2.png
The values in the orange zone should range from 1.0E+11 to 5.0 E+11, which is not the case by two orders of magnitude ! Actually by multiplying the values by a factor of about 500 the result matches quite well with the isolines. How can this be explained?
I thank you warmly in advance for your answer.
FPP
barbara.stunder
Posts: 439
Joined: November 9th, 2012, 4:23 pm
Registered HYSPLIT User: Yes

Re: Differences between results at different output resolutions and discrepancy between ascii values and corresp. contou

Post by barbara.stunder »

The contours in concplot are smoothed, so yes, there can be differences in the details you are looking at.  Please plot using the hysplit utility program gridplot, which does not do contouring, it just plots the values on the grid.  The program gridplot is in the PC distribution.  

In your figure with Aspect 1 - is the plume width nearest the source the same as the grid resolution for both resolutions?   In HYSPLIT, using a smaller concentration grid will better represent the plume very close to the (point) source.  You can use a smaller grid than the meteorology, but realize the meteorology is linearly interpolated in space and time.  

There is uncertainty in the meteorology, so if the real wind direction were slightly different, or the speed, the footprint would be different hence in your application different people being affected.  

How does the concentration averaging time compare to the time interval of the meteorology?  This can also affect the concentration values at the detail you are looking at.
fppiguet
Posts: 8
Joined: June 18th, 2018, 9:25 am
Registered HYSPLIT User: Yes

Re: Differences between results at different output resolutions and discrepancy between ascii values and corresp. contou

Post by fppiguet »

We thank you warmly for your answer.
Best regards
Frederic
Post Reply