[MITgcm-support] 2D model - Varying cell width (delY)

[Martin Losch]

Hi Pascal,

if you don’t want to get your hands dirty, then you can choose the curvilinear grid option. That’s a bit complicated, because you’ll have to compute all sorts of grid files offline. You can find an example of the required files and how to read them here: http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/arctic … something (the server appears to be down currently, so I cannot point you to the exact place). One needs to define OLD_GRID_IO and then provide dx,dy,etc. (see ini_curvilinear_grid.F for details). Constant f or beta plane also needs to be specficied explicity by fields for coriolis (selectCoriMap=3, see ini_cori.F)

For a cartesian grid, it’s probably safe to simply hardwire dyG and dyF in ini_cartesian_grid.F 

But note that with just one row of grid cells you’ll have periodic boundary conditions in y (i.e. no walls). For a wall you need a second row of grid cells with bathymetry=0

Martin


> On 13. Nov 2020, at 20:21, Pascal Bourgault <pascal.bourgault at gmail.com> wrote:
> 
> Hi!
> 
> I am currently working on a 2D model (X and Z) of an estuary with the MITgcm. My goal was to simplified the problem by ignoring lateral advection, horizontal eddies and lateral variation of the bathymetry, while keeping the vertical shear- and bathymetry-induced mixing. So I have a 1 m Δz and a telescopic Δx, going from 65 m to 20 m in the center and back to ~ 120 m at the mouth of the estuary, where I use OBCS to prescribe T, S and U.
> 
> One problem we are currently having is that Δy is constant. There is a single y row of 50 m (a number chosen so that the Δx/Δy ratio stays reasonable throughout the regions of interest). That means that only the bathymetry makes the cross-section area vary along the estuary. In order to get something a bit more realistic, I was wondering if there was a way to have a varying Δy in the model? AFAIU, that means having dyF a function of x (and not only of y). As long as I stay with 1 row of cells, it would be geometrically sane, but is it doable in the MItgcm?
> 
> I am ready to get my hands dirty and to dig a bit in the code, but I would like to have the opinion of experts. Where should I modify the source? I see that "/model/src/ini_cartesian_grid.F" is a good start, but I expect it to be a bit more difficult than that?
> 
> I am currently trying the solution of having a few rows in y and putting walls to simulate the narrowing of the channel. However, that adds a lot of computation and creates "singularities" since the variation of Δy isn't smooth at all.
> 
> 
> Thanks!
> 
> --
> Pascal Bourgault
> 
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