[MITgcm-support] some problems about curvilinear grid

[Martin Losch]

Dear Liangjun Yan,

I am not quite sure if I understand the problem.
As far as I know, AngleCS and AngleSN are never really used in the model, but they are a “service” to the user. That is, if they are wrong it doesn’t matter for the simulation.

Having said that, it would still be great if these quantities are correct. So if you can provide a simple example (small number of grid points), that you can share (please only send a link, not a the files).

For your immediate problem: both methods should be OK, so I’d go for method (1), because it’s simpler.

Martin

> On 24. Oct 2019, at 04:05, <liangjun.yan at hhu.edu.cn> <liangjun.yan at hhu.edu.cn> wrote:
> 
> Hi everyone
> 
> I am trying to run a regional model in Ross sea with the curvilinear grid. But I encounter a problem, that is, the AngleCS and AngleSN generated by the model will have an abrupt change at the north (last column)/east (last row) boundaries. In other words, the value of AngleCS and AngleSN should be as close to the adjacent column/row as the other columns/rows at the last columns/rows. But the AngleCS mostly going to be 1/0, AngleSN close to 0/1.
> 
> We conduct a few tests to figure out what happened, and read some code then we found some results. If the latitude of the region we selected were symmetric, the AngleCS and AngleSN file would be fine everywhere (e.g., the Pan–Antarctica region with latitude and longitude shown in Figure 1 and Figure 2). But If the domain only contains one half of the Antarctica (e.g., the half longitude from 0E to 180E), we find that only the northern boundary (last column) has the sharp changes in the AngleCS/SN and the eastern boundary (last row) changes smoothly as expected.
> 
> At the current stage, I think I may try to use the following two methods to avoid the sharp changes of the angle value at the northern and eastern boundaries as follows:
> 
> 1) I can use the AngleCS and AngleSN data of the penultimate row and the penultimate column at the northern or eastern boundaries;
> 
> 2) I can create a larger domain and take out the AngleCS and AngleCS data in my smaller domain where I am interested.
> 
> However, I still want to know what causes this problem, and whether the two methods mentioned above are correct, since I have to apply these angle file to my prescribed open boundary conditions. I am really appreciated to any help and suggestions.
> 
>  <Fig1.tif><fig2.tif><fig3.tif><fig4.tif>
> 
> Best regards, 
> 
> Liangjun Yan
> 
> Master student, Physical Oceanography
> 
> Liangjun.yan at hhu.edu.cn
> 
> NO.1, Xikang Road, Nanjing, 210098，China
> 
> Hohai Universuty
> 
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