Discussion about analysis, visualization, and collaboration tools and techniques

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susonic
Posts: 160
Joined: Tue Aug 21, 2007 5:44 pm
Location: Jeju National University
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Dear ROMS users,

I was wondering why we set minimum depth in ROMS ?

arango
Posts: 1114
Joined: Wed Feb 26, 2003 4:41 pm
Location: IMCS, Rutgers University
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Look at the governing equations and think about its spatial discretization in numerical models. What would happen if you have a grid cell with zero depth? What are the values of the vertical level thicknesses?

I gave you a good clue... As a homework, you can figure out the rest...

susonic
Posts: 160
Joined: Tue Aug 21, 2007 5:44 pm
Location: Jeju National University
Contact:

So, we have to set non-zero value as a minimum depth in order not to make the vertical level thickness zero.

-JH

arango
Posts: 1114
Joined: Wed Feb 26, 2003 4:41 pm
Location: IMCS, Rutgers University
Contact:

Yes, that's part of the answer. But you still have to check the governing equations. If the vertical thickness (Hz) is zero, what would happen to the vertical viscosity and diffusion terms? Then if you search for oHz in the code, you will notice that the internal array oHz is in several routines of the numerical kernel. Notice that oHz=1/Hz.

This is the kind of analysis that users with curiosity need to carry out to discover what are the assumptions that we need to make when coding the continuum governing equations in numerical models. This kind of analysis is needed to determine was is the appropriate minimum depth (hmin) for a particular application, for instance. This is going to control the vertical time step limitation (CFL) as a function of your specified number of vertical levels. In terrain-following coordinates, we need to have all the vertical levels to exist at the minimum depth.

So now you know why we cannot have a water column with a total thickness of zero

I added an entry to the FAQ web page of WikiROMS and hope that this issue is very clear and never discussed again in the forum.

susonic
Posts: 160
Joined: Tue Aug 21, 2007 5:44 pm
Location: Jeju National University
Contact:

Thank you for your detailed comment and adding an entry of WikiROMS.
That is kind of you to do so.
And I'm sure that users can get this fundamental information via the WikiROMS.

Regards,

-JH

Lei_Shi
Posts: 4
Joined: Thu Aug 14, 2003 7:46 pm
Location: School of Marine Science, University of Maine