How small are the "large water bodies" that NEMO can simulate

Versions v4.2.x
1

I am trying to refine a global coupled model I have developed.
Somewhere in one of the NEMO manuals it says,
" When a global ocean is coupled to an atmospheric model it is better to represent all large water bodies (e.g, great lakes, Caspian sea…) even if the model resolution does not allow their communication with the rest of the ocean. This is unnecessary when the ocean is forced by fixed atmospheric conditions, so these seas can be removed from the ocean domain. The user has the option to set the bathymetry in closed seas to zero (see §15.2), but the code has to be adapted to the user’s configuration.”

I am currently thinking of doing this manually by editing an ORCA025 configuration to agree better with my atmospheric grid that treats the Caspian Sea and many smaller bodies of water as ocean. I have implemented a 0-d column model to handle slight mismatches at coastlines and small closed bodies of water, but I’d like NEMO to simulate larger closed bodies of water.

Does anyone have a sense of how big the body of water needs to be? I’d like to avoid instabilities, so I’m going to avoid straits etc. But I’m not sure if Lake Baikal (long and thin) is too thin (~ 2 grid points) to simulate in NEMO.

Thanks for any insights,

Nick

2

So the solution appears to be that closed ocean areas smaller than ~ 10 points are likely to produce instabilities.

3

The stability will depend on the fluxes you apply of your “water body”. For example if you evaporate all the water of your small “water body” with may be a problem… sbcclo can be used to avoid this kind of problems.

Another issue is when you create “water bodies” too close from ORCA grid northern poles (in Siberia and in Canada), where the grid size can become very small.