What is SORT-INDEX in the PARDUMP format?

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

What is SORT-INDEX in the PARDUMP format?

Post by wsr » October 8th, 2018, 6:03 pm

The particle output parameter SORT-INDEX does not appear to be described in the Hysplit user guide. Can anyone state definitively what SORT-INDEX represents for each particle and how it is used, specifically in a multi-processor run?

alicec
Posts: 87
Joined: February 8th, 2016, 12:56 pm
Registered HYSPLIT User: Yes

Re: What is SORT-INDEX in the PARDUMP format?

Post by alicec » October 10th, 2018, 3:18 pm

The sort index is used within HYSPLIT for looping through all the computational particles or puffs. It was not intended to be a unique identifier of
computational particles.

Computational particles:
If a computational particle is removed during the simulation, the sort indices are reassigned so that there are only as many sort indices as particles.

Consequently, the sort index for a computational particle may change during a simulation. If ichem=8, then particle deletion is turned off, and the sort index will refer to the same computational particle throughout the simulation.
Also, if you ensure that no particles are ever removed during a simulation, the sort index should stay the same throughout the simulation.
The most common way for particles to be removed is if they go off all specified meteorological grids. Having at least one global met dataset would prevent this. Other ways for particles to be removed are if KHMAX is specified or ichem=5.
https://ready.arl.noaa.gov/hysplitusersguide/S623.htm
https://ready.arl.noaa.gov/hysplitusersguide/S628.htm

Computational puffs
In the case of puffs, the sort indices are reassigned when puffs change position are deleted or split or merged. Consequently the
sort index cannot be used to keep track of puffs.

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