[Bug]: angle_dx field in the Arctic domain is wrong

[kshedstrom]

Contact Details

No response

What happened?

It ranges from zero to pi:

!

How to replicate?

View angle_dx. I did a grep for 'angle_dx' and can't find that it is used anywhere. Is it?

Relevant log or error output

No response

global attributes

No response

[jr3cermak]

This was apparently fixed by uncommenting a section of code shown below.

If converting a ROMS grid to a MOM6 grid:

gridtools/gridtools/grids/mom6.py

Lines 749 to 758 in 6764e65

	angle = numpy.zeros(lat.shape)
	angle2 = numpy.zeros(lat.shape)
	# angle[:,1:-1] = numpy.arctan2( (lat[:,2:] - lat[:,:-2]) , ((lon[:,2:] - lon[:,:-2]) * cos_lat[:,1:-1]) )
	# angle[:, 0 ] = numpy.arctan2( (lat[:, 1] - lat[:, 0 ]) , ((lon[:, 1] - lon[:, 0 ]) * cos_lat[:, 0 ]) )
	# angle[:,-1 ] = numpy.arctan2( (lat[:,-1] - lat[:,-2 ]) , ((lon[:,-1] - lon[:,-2 ]) * cos_lat[:,-1 ]) )
	lon = numpy.where(lon < 0., lon+360, lon)
	angle2[:,1:-1] = numpy.arctan2( (lat[:,2:] - lat[:,:-2]) , ((lon[:,2:] - lon[:,:-2]) * cos_lat[:,1:-1]) )
	angle2[:, 0 ] = numpy.arctan2( (lat[:, 1] - lat[:, 0 ]) , ((lon[:, 1] - lon[:, 0 ]) * cos_lat[:, 0 ]) )
	angle2[:,-1 ] = numpy.arctan2( (lat[:,-1] - lat[:,-2 ]) , ((lon[:,-1] - lon[:,-2 ]) * cos_lat[:,-1 ]) )
	self.mom6_grid['supergrid']['angle'][:,:] = numpy.maximum(angle, angle2)

Uncomment lines 751-753, regenerate the MOM6 grid and check the angles again. A future release will document an additional keyword argument to pass to trigger the alternate calculation of the angle. It is not clearly understood the conditions that require the alternate calculation of the angle. By default, the gridtools library will maintain its current behavior.

If creating a MOM6 grid for the first time, this code needs to be altered:

gridtools/gridtools/gridutils.py

Lines 568 to 582 in 6764e65

	# Presize the angle_dx array
	angle_dx = np.zeros(lat.shape)
	angle2_dx = np.zeros(lat.shape)
	# This was commented out in the original conversion code?
	#angle_dx[:,1:-1] = np.arctan2( (lat[:,2:] - lat[:,:-2]) , ((lon[:,2:] - lon[:,:-2]) * cos_lat[:,1:-1]) )
	#angle_dx[:, 0 ] = np.arctan2( (lat[:, 1] - lat[:, 0 ]) , ((lon[:, 1] - lon[:, 0 ]) * cos_lat[:, 0 ]) )
	#angle_dx[:,-1 ] = np.arctan2( (lat[:,-1] - lat[:,-2 ]) , ((lon[:,-1] - lon[:,-2 ]) * cos_lat[:,-1 ]) )
	# Fix lon so they are 0 to 360 for computation of angle_dx
	lon = np.where(lon < 0., lon+360, lon)
	angle2_dx[:,1:-1] = np.arctan2( (lat[:,2:] - lat[:,:-2]) , ((lon[:,2:] - lon[:,:-2]) * cos_lat[:,1:-1]) )
	angle2_dx[:, 0 ] = np.arctan2( (lat[:, 1] - lat[:, 0 ]) , ((lon[:, 1] - lon[:, 0 ]) * cos_lat[:, 0 ]) )
	angle2_dx[:,-1 ] = np.arctan2( (lat[:,-1] - lat[:,-2 ]) , ((lon[:,-1] - lon[:,-2 ]) * cos_lat[:,-1 ]) )
	self.grid['angle_dx'] = (('nyp', 'nxp'), np.maximum(angle_dx, angle2_dx))

Uncomment lines 573-575.

This only applies to spherical grids.