Questiion about Nested Grids & Land Masking

[bhayward]

Hello,

I think I have been using masking incorrectly in my refined grid (and I think I understand now), but I wanted to make a post to double check and ask a further question.

If we don't want the model to simulate a point, we set the land mask to 0. That can be because there is land there, or it is already being modelled by another grid; but if we want it to be ignored, it should be set to 0. In this image of Espresso's grids (from the ROMS Wiki Page for Nested grids, https://www.myroms.org/wiki/File:Delawa ... e_zoom.png), The colored boxes are where the land mask is 1, and the water is modelled.

514px-Delaware_Chesapeake_zoom.png (422.44 KiB) Viewed 131 times

What's going on here in the NestLayer above this? Are the bays masked, so that the refined grids do the work?

I've been using refined grids, with 1 coarse and 1 fine, and have been having issues with my estuaries. Most of this has been the normal "slope too large" problem, but recently, I had a blowup in the coarse grid, in a location where the fine grid was working well.

Assuming I do change the coarse grid's masking, should I recreate the contact region? I think the contact region generation is independent of the mask, but I am not entirely sure.

Thank you for your time.

-Ben

[wilkin]

Are you 1-way or 2-way nesting?

In 2-way nesting, the coarse grid solution is replaced with a simple average of the fine grid, and what the coarse grid computed in that region is immaterial to the solution you will see, but ROMS still runs the coarse grid solution for one coarse time step so it is possible for some bad things to happen.

You need to pay a bit of attention to the match-up of fine and coarse land masks so that the fine2coarse step can do something sensible with the average.