On our eORCA025 config, NEMO v4.0.1 with jperio == 4. The first two and last two columns (x dims) are the same due to east-west cyclicity.
Then, my understanding is that each wet cell on the
j == jpjglo row has exactly one twin on the other side (here “other side” is with respect to grid index
i) of the North American continent, on the
j == jpjglo - 1 row. No other cells are duplicated, and no cell is there three times. At least that’s what comes out when searching for geographical duplicates in our mesh_mask files.
Is that correct with jperio == 4? Got confused because because if it is, then I don’t get this line of the CDFTOOLS sea-ice diagnostics:
CASE (4) ! ORCA025 type boundary
It’s meant to compute integrated sea-ice metrics (volume, extent etc.). The code above masks the duplicated cells to avoid double accounting: first the east-west cyclicity duplicates, then the top row, and finally one half of the second-to-top row. I don’t get that last step - seems to me that it’s removing an extra half-row… but I want to be sure that it’s not due to some inconsistencies between
jperio and our coordinate files.
About North Pole Folding: you may find these sketches useful (thanks to Seb), Migrating from 4.0.x to 4.2.x — NEMO release-4.2.0 documentation
You have a “T-point” folding, i.e. the symmetry at T-points concerns 3 lines along j ; the center (invariant) of the transform is located at the T-point located at
(ip = npiglo/2 + 1 ; jp = npjglo-1). Hence, row at
j=npjglo-1 is symmetric along
i around this point. So it makes sense counting points only once for half of this line.
This said, I would have rather written in the block above:
e.g. kept the pivot as part of “non-duplicated” points.
@smasson, aka “NEMO NPF master”, would easily confirm this or not.
NB: Everything above is based on Fortran indexing
Many thanks Jérôme, and thanks to the person (presumably the NEMO NPF master) who made these new sketches. So if I got it right:
jperio == 4:
- every cell on the
j=npjglo-1 line has a symmetric on the same line;
- every cell on the
j=npjglo line has a symmetric on the
jperio == 6: every cell on the
j=npjglo has a symmetric on the
j=npjglo-1 line, and that’s it.
You got it (there is aditionnal complexity for vector fields of course).
I wrote too fast. Of course, it should rather be;