Boundary condition at ground level

Topics about the HYSPLIT dispersion model.
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lagom
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Boundary condition at ground level

Post by lagom »

Hi everybody,

I have a question, is it possible to use a simple boundary condition such that when a particle reach the ground its evolution ends and its landing position is saved? A sort of deposition without activating the deposition model.

thank you in advance

D.
ariel.stein
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Re: Boundary condition at ground level

Post by ariel.stein »

You could set your deposition velocity to a very high number in such a way that if the particles are below the surface layer it will completely deplete their mass.
lagom
Posts: 16
Joined: January 25th, 2016, 4:00 am
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Re: Boundary condition at ground level

Post by lagom »

Thank you for the suggestion but if I start the emission close to ground I think that with a very high deposition velocity all particles would be deposited immediately, because deposition is turned on in the surface layer (which default height is 75m in the model).
I would like to set the model such that particles are deposited when they reach the ground and not in the entire surface layer.

thank you

D.
lagom
Posts: 16
Joined: January 25th, 2016, 4:00 am
Registered HYSPLIT User: Yes

Re: Boundary condition at ground level

Post by lagom »

Thank you for the suggestion but if I start the emission close to ground I think that with a very high deposition velocity all particles would be deposited immediately, because deposition is turned on in the surface layer (which default height is 75m in the model).
I would like a model set up in which particles are deposited when they reach the ground level and not in the whole surface layer.

thanks

D.
ariel.stein
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Re: Boundary condition at ground level

Post by ariel.stein »

The normal deposition mode is for particles to loose mass to deposition when those particles are within the deposition layer.
An additional option was added to deposit the entire particle's mass at the surface (the particle is removed) when subjected to deposition.
To insure the same mass removal rates between the two methods, a probability of deposition is computed, so that only a fraction of the
particles within the deposition layer are deposited in any one time step. The probability of deposition is a function of the deposition velocity,
time step, and depth of the layer. One limitation of this method is that only one mass species may be assigned to a particle. The probability
deposition method can be invoked from the namelist file with ICHEM=5.
lagom
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Re: Boundary condition at ground level

Post by lagom »

Ok, but what layer are we dealing with? Is it the surface layer (second internal model layer usually set around 75m heigh )? It is possible to set its thickness?

Thank you for the reply

D.
ariel.stein
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Re: Boundary condition at ground level

Post by ariel.stein »

Yes, we are still dealing with the surface layer (~75 m).
No, unfortunately that cannot be changed.
lagom
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Re: Boundary condition at ground level

Post by lagom »

Ok, thank you for clarifying my doubts.
Don't you think that keeping a fixed value for the surface layer height can be a too strong restriction?

Thanks for your replies

D.
ariel.stein
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Re: Boundary condition at ground level

Post by ariel.stein »

If you think that there is scientific evidence that changing that value will improve the performance of the model please let us know so we can incorporate such changes in the code.
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