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Tripolar lines in velocity plot - Arctic view #53

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VanessaSutton-Pande opened this Issue Aug 3, 2017 · 8 comments

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VanessaSutton-Pande commented Aug 3, 2017

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Jeffreydaw commented Aug 4, 2017

as seen in this screen grab, there are lines are visible in the pole projection. this seems to be the result of a misinterpretation of the around the pole possibility because of the tripolar projection used in the GIOPS data.
selection_023

and as can be seen here the arrows do not line up as expeced around the lines.
selection_024

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Jeffreydaw commented Sep 1, 2017

The tripolar grid dose does not come into effect till 40deg north so the problem is probably only above that. This is backed up by the fact that the Labrador current and the currents by Japan both seem to be pointing the correct directions

@Jeffreydaw Jeffreydaw self-assigned this Sep 5, 2017

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Jeffreydaw commented Sep 5, 2017

@Jeffreydaw Jeffreydaw changed the title from lines in velocity plot - Arctic view to Tripolar lines in velocity plot - Arctic view Jan 8, 2018

@nsoontie nsoontie self-assigned this Jan 26, 2018

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nsoontie commented Feb 2, 2018

The tripolar lines are an artifact of the rotation of the GIOPS grid lines. Above about 40 deg N, the x grid lines are no longer aligned east/west.

giops_grid_angle
giops_grid_angle_polar

We can correct this issue by calculating the angle between the xgrid lines and east, and then rotating the velocity fields upon loading. The angle can be computed once for each grid and saved in a netcdf file listed in the model's config file.

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Jeffreydaw commented Feb 28, 2018

This problem can also be seen in GLORYS but the lines are a little different.

tri_polar_glorys

navigator link

see page 40 of PRODUCT USER MANUAL to see the used grid (I belive that is the correct product manual)

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nsoontie commented Mar 7, 2018

grid_angle.nc files created for riops (usergrid), giops, salishsea, gulf and glorys

Note: Glorys needs to be interpolated to A-grid

Next step: Write config files and code for handling rotation.

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nsoontie commented Apr 4, 2018

There are still minor errors for velocities at the northfold on ORCA grids. These errors are small, ~1% and can be seen in the test_giops_east, north, north_east datasets.

The errors are a result of the rotation. I will investigate further.

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Jeffreydaw commented Jul 19, 2018

The fix of pre-rotating the files seems to have caused problems with the THREDDS server. the change was reverted and we need to explore other options

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