Open dougiesquire opened 1 week ago
It looks like the ESM1.5 ice + ocean grids are consistent with each other, so that's good? Whats the advantage in the new format?
(EDIT: we should be able to get 1e-13 accuracy between ice & ocn grids by regenerating)
It seems that calculating the areas near a pole is... complex. See
poly_area
function used in FRE-NCTools' transfer_to_mosaic_grid
to calculate the areasIt looks like a fix was made in FRE-NCtools.
Does one of the versions of the grids have an obvious jump / discontinuity in areas around the true north pole?
It looks like a fix https://github.com/NOAA-GFDL/FRE-NCtools/pull/60 in FRE-NCtools.
I built FRE-NCTools from source yesterday (i.e. including that bug fix) and converted the ESM1.5 grid to a mosaic spec that had areas that match the OM2 grid. So that fix doesn't resolve our issue.
Both the ESM1.5 and OM2 grid areas have a small jump across the north pole, but it's slightly smaller in the OM2 grid...? See the notebook above for details.
This plot shows the area of OM2 grid (orig) and the newly generated (new) using make_hgrid
grid at the north pole along the longitude direction. The left plot shows the area symmetry error.
plt.plot(Orig05['area'][-1,:], label='orig' )
A big spike at the tripoles shows the abnormalities in cell area in the existing OM2 grid and new grid. I tried generating the grid using --rotate_poly
, which calculates the area of polygons near the pole using a copy of the polygon that has been rotated away from the pole. It resolves the abnormal area spike however it Introduces a big area symmetry error compared to the original one without --rotate_poly
(left plot). Even though the error is of the magnitude of ~2e-6% (3m2 error on ~1.5e8 m2) still it we need to think about what can be done, @ofa001 and @DaveBi any thoughts on this?
PS - Area symmetry error is calculated at the north pole as following:
plt.plot( New05['area'][-1,:] - New05['area'][-1,::-1], label='new' );
plt.plot( Orig05['area'][-1,:] - Orig05['area'][-1,::-1], label='orig' );
Note, --rotate-poly
is not an option for transfer_to_mosaic_grid
but I modified FRE-NCtools to add it. As @ezhilsabareesh8 shows using make_hgrid
, this gets rid of the spike at the pole. See the notebook linked in my first post for details.
Good catch re the increase in symmetry errors @ezhilsabareesh8.
These configurations use an old FMS format to specify the ocean grid. Can/should we update to use the new mosaic format? Can we just use the mosaic from the ACCESS-OM2 1 deg configurations?
This notebook includes some checks to help us answer these questions.
To summarise:
transfer_to_mosaic_grid
. Converting the ESM1.5 grid to the mosaic format usingtransfer_to_mosaic_grid
gives areas that match OM2.So, we could update the ocean grid to use the same file as the OM2 1 deg configuration, but this will change cell areas slightly which will presumably change results. Does this mean we should leave this for a subsequent release?