LLC4320 SSU/SSV data at Pangeo cloud mismatched

Since access to LLC4320 from ECCO portal is too slow, I’m using LLC4320 data at pangeo cloud for my research.

However, it seems that the SSU/SSV variable of LLC4320 is wrongly mismatched at Pacific Ocean.

U/V from Pangeo cloud

And here is the right one from ECCO portal:

U/V from ECCO portal

In order to create the first set of figures, you have to assemble the 13 faces in the dataset into a world map. How are you doing that? Are you using llcreader? That is what I recommend. If yes, which version of llcreader are you using (and please supply a few lines of code)?

By design, U points in the i direction and V points in the j direction on each of the individual faces. Because i and j do not line up with latitude and longitude on some faces, you need llcreader to do a transformation in order to get a map that makes sense. We have had errors with this in the past, but my impression is that they have been fixed.

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I use xmitgcm.llcreader for process. The xmitgcm version is 0.5.2.
Here is the code to create the first figure:

import numpy as np
import xarray as xr
from xmitgcm import llcreader
import matplotlib.pyplot as  plt

from intake import open_catalog
cat = open_catalog("")

# Get variables from catalog
grid = cat.LLC4320_grid.to_dask()
sst = cat.LLC4320_SST.to_dask()
u = cat.LLC4320_SSU.to_dask()
v = cat.LLC4320_SSV.to_dask()

ds = xr.merge([grid,sst, u, v])
ds = llcreader.llcmodel.faces_dataset_to_latlon(ds, metric_vector_pairs=[('dxC', 'dyC'), ('dyG', 'dxG')])

fig = plt.figure(figsize=[16,10])
ax = fig.add_subplot(211)
ax = fig.add_subplot(212)
# fig.savefig("pangeo.png",dpi=600)

I looked into this further, and it seems you are describing a known issue that happens because some of the metadata is missing. Please read through this thread: to_latlon does not rotate velocities · Issue #216 · MITgcm/xmitgcm · GitHub and use the hack provided by @dhruvbalwada .

OK, it did work. Thank you so much!