Finite divergence for bolus velocity in the first two verical layer near land about gcmfaces

[MaceKuailv]

BTW, it does not make a difference if one includes hFacS and hFacW

ds['utrans'] = (ds['UVELSTAR']*ds['drF']*ds['dyG']*ds['hFacW']).fillna(0)
ds['vtrans'] = (ds['VVELSTAR']*ds['drF']*ds['dxG']*ds['hFacS']).fillna(0)

[MaceKuailv]

I tried to use xgcm for the same calculation,

strm = xr.open_dataset('OCEAN_BOLUS_STREAMFUNCTION_day_mean_1992-01-01_ECCO_V4r4_native_llc0090.nc')

strmx = strm.GM_PsiX.fillna(0)
strmy = strm.GM_PsiY.fillna(0)

u = xgcmgrd.diff(strmx,"k", boundary = 'fill', fill_value = 0.0)/ds.drF
v = xgcmgrd.diff(strmy,"k", boundary = 'fill', fill_value = 0.0)/ds.drF

vstrmx = strmx*ds.dyG
vstrmy = strmy*ds.dxG

xy_diff = xgcmgrd.diff_2d_vector(
    {"i": vstrmx, "j": vstrmy}, boundary="fill", fill_value=0.0
)
x_diff = xy_diff["i"]
y_diff = xy_diff["j"]
hDiv = (x_diff + y_diff) 

w = hDiv/ds.rA

When I plug this into the divergence calculation above, the divergence is very small. The horizontal components are the same but the vertical velocity at the second level are different.

diffu = (u - ds.UVELSTAR).fillna(0)
diffv = (v - ds.VVELSTAR).fillna(0)
diffw = (w - ds.WVELSTAR).fillna(0)
plt.imshow(diffw[0,1,10].T)
plt.colorbar()

which yields:

[gaelforget]

@ifenty @owang1 can you help with this? It relates to python toolboxes and ECCOv4r4 which you know better than me

[MaceKuailv]

Thank you! Let me know if there is anything that I could help.

[owang01]

Thanks @gaelforget

@MaceKuailv Thank you for the detailed description and the Python code regarding the issue. I will look into it and get back to you.