Extract particle path (start/stop) information

Topics about the HYSPLIT dispersion model.
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wsr
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Joined: August 23rd, 2017, 12:08 am
Registered HYSPLIT User: No

Extract particle path (start/stop) information

Post by wsr » October 1st, 2018, 8:59 pm

I am running the dispersion model in a multi-processor environment.

I am interested in the particle path time series that Hysplit generates. I do not need the entire path, but I need to be able to associate the initial condition with the final location listed in, say, a PARDUMP file.

The problem I am running into is that Hysplit does not write the particle locations to the PARDUMP file in the same order as the initial conditions. It seems to sort them vertically in some sense, and keeps latitude/longitude clusters together.

The obvious solution is to run Hysplit many times, once for each specific starting location: then there is no ambiguity. This is suboptimal for two reasons: (1) the same random numbers will be used to simulate diffusion each time, introducing artificial correlation among particles of different runs, and (2) then we are essentially running Hysplit in serial mode, sacrificing much of the performance gain.

I am having trouble digging into the source to find out where the particle sorting/re-ordering takes place. It makes sense that it would occur prior to running the forward model in order to optimize the performance of a semi-Lagrangian simulation. It also might occur between each timestep.

Can someone suggest a simpler alternative to getting this particle path information that does not sacrifice performance, such as a Hysplit configuration setting I may have overlooked? Otherwise, can one of the developers/maintainers help me identify the subroutines where the sorting is taking place? If I can do that, then I can track and dump a mapping to the original particle input order.

alicec
Posts: 101
Joined: February 8th, 2016, 12:56 pm
Registered HYSPLIT User: Yes

Re: Extract particle path (start/stop) information

Post by alicec » October 9th, 2018, 10:42 am

In July 2018 an option was added to output particle positions at the simulation start to the PARDUMP file.
See:
https://ready.arl.noaa.gov/hysplitusersguide/S627.htm

NDUMP=0, NCYCL=+N
Particle positions written at simulation start then again at 1*N, 2*N, 3*N
NDUMP=0, NCYCL= -N
Particle positions written at simulation start and each time step up to hour N


Possibly this will solve your problem?

alicec
Posts: 101
Joined: February 8th, 2016, 12:56 pm
Registered HYSPLIT User: Yes

Re: Extract particle path (start/stop) information

Post by alicec » October 10th, 2018, 4:09 pm

Please note that this option to output initial positions in the pardump file was implemented in v972.

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Renee.Degutis
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Re: Extract particle path (start/stop) information

Post by Renee.Degutis » December 3rd, 2018, 2:04 am

Hello,

Is there a simple way to convert the particle position file to a concentration file? What input parameters should we use then?

Thank you,
Renee

alicec
Posts: 101
Joined: February 8th, 2016, 12:56 pm
Registered HYSPLIT User: Yes

Re: Extract particle path (start/stop) information

Post by alicec » December 3rd, 2018, 10:24 am

If you need concentration files, then for most applications it is best to just setup your HYSPLIT run to produce the concentration
files you need rather than to produce particle position files and convert them.

There is a command line utility called par2conc which will convert pardump (particle position) files to cdump (concentration) files.
It is not available through the GUI. You can find it in the exec directory.

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