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Extend spatial slip condition to lower Z faces #3044

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0e14848
Update _xinterpolators.py: Extend spatial slip to lower Z faces
paolobellinopasquali Nov 5, 2026
486a16c
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 5, 2026
a49f405
Add tests for spatial slip on lower Z faces
paolobellinopasquali Nov 8, 2026
3272f4a
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 8, 2026
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36 changes: 30 additions & 6 deletions src/parcels/interpolators/_xinterpolators.py
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Original file line number Diff line number Diff line change
Expand Up @@ -409,11 +409,19 @@ def _Spatialslip(

corner_dataU = _get_corner_data_Agrid(vectorfield.U.data, ti, zi, yi, xi, lenT, lenZ, npart, axis_dim)
corner_dataV = _get_corner_data_Agrid(vectorfield.V.data, ti, zi, yi, xi, lenT, lenZ, npart, axis_dim)
corner_dataW = None
if vectorfield.W:
axis_dimW = vectorfield.W.grid.get_axis_dim_mapping(vectorfield.W.data.dims)
corner_dataW = _get_corner_data_Agrid(vectorfield.W.data, ti, zi, yi, xi, lenT, lenZ, npart, axis_dimW)

def is_land(ti: int, zi: int, yi: int, xi: int):
uval = corner_dataU[ti, zi, yi, xi, :]
vval = corner_dataV[ti, zi, yi, xi, :]
return np.where(np.isclose(uval, 0.0) & np.isclose(vval, 0.0), True, False)
wval = None if corner_dataW is None else corner_dataW[ti, zi, yi, xi, :]
land_check = np.isclose(uval, 0.0) & np.isclose(vval, 0.0)
if wval is not None:
land_check = land_check & np.isclose(wval, 0.0)
return np.where(land_check, True, False)

if is_dask_collection(u):
u = u.compute()
Expand All @@ -434,6 +442,10 @@ def is_land(ti: int, zi: int, yi: int, xi: int):
land = is_land(0, 0, 1, 0) & is_land(0, 0, 1, 1) & is_land(0, 1, 1, 0) & is_land(0, 1, 1, 1) & (eta < 1)
f_u[land] = f_u[land] * (1 - b * eta[land]) / (1 - eta[land])

if lenZ == 2:
land = is_land(0, 1, 0, 0) & is_land(0, 1, 0, 1) & is_land(0, 1, 1, 0) & is_land(0, 1, 1, 1) & (zeta < 1)
f_u[land] = f_u[land] * (1 - b * zeta[land]) / (1 - zeta[land])

u = u * f_u
if vectorfield.grid.mesh.is_spherical():
u /= 1852 * 60 * np.cos(np.deg2rad(particle_positions["y"]))
Expand All @@ -451,24 +463,36 @@ def is_land(ti: int, zi: int, yi: int, xi: int):
land = is_land(0, 0, 0, 1) & is_land(0, 0, 1, 1) & is_land(0, 1, 0, 1) & is_land(0, 1, 1, 1) & (xsi < 1)
f_v[land] = f_v[land] * (1 - b * xsi[land]) / (1 - xsi[land])

if lenZ == 2:
land = is_land(0, 1, 0, 0) & is_land(0, 1, 0, 1) & is_land(0, 1, 1, 0) & is_land(0, 1, 1, 1) & (zeta < 1)
f_v[land] = f_v[land] * (1 - b * zeta[land]) / (1 - zeta[land])

v = v * f_v
if vectorfield.grid.mesh.is_spherical():
v /= 1852 * 60

if vectorfield.W:
f_w = np.ones_like(zeta)
land = is_land(0, 0, 0, 0) & is_land(0, 0, 0, 1) & is_land(0, 1, 0, 0) & is_land(0, 1, 0, 1) & (eta > 0)
last_z = lenZ - 1
land = (
is_land(0, 0, 0, 0) & is_land(0, 0, 0, 1) & is_land(0, last_z, 0, 0) & is_land(0, last_z, 0, 1) & (eta > 0)
)
f_w[land] = f_w[land] * (a + b * eta[land]) / eta[land]

land = is_land(0, 0, 1, 0) & is_land(0, 0, 1, 1) & is_land(0, 1, 1, 0) & is_land(0, 1, 1, 1) & (eta < 1)
land = (
is_land(0, 0, 1, 0) & is_land(0, 0, 1, 1) & is_land(0, last_z, 1, 0) & is_land(0, last_z, 1, 1) & (eta < 1)
)
f_w[land] = f_w[land] * (1 - b * eta[land]) / (1 - eta[land])

land = is_land(0, 0, 0, 0) & is_land(0, 0, 1, 0) & is_land(0, 1, 0, 0) & is_land(0, 1, 1, 0) & (xsi > 0)
land = (
is_land(0, 0, 0, 0) & is_land(0, 0, 1, 0) & is_land(0, last_z, 0, 0) & is_land(0, last_z, 1, 0) & (xsi > 0)
)
f_w[land] = f_w[land] * (a + b * xsi[land]) / xsi[land]

land = is_land(0, 0, 0, 1) & is_land(0, 0, 1, 1) & is_land(0, 1, 0, 1) & is_land(0, 1, 1, 1) & (xsi < 1)
land = (
is_land(0, 0, 0, 1) & is_land(0, 0, 1, 1) & is_land(0, last_z, 0, 1) & is_land(0, last_z, 1, 1) & (xsi < 1)
)
f_w[land] = f_w[land] * (1 - b * xsi[land]) / (1 - xsi[land])

w = w * f_w
else:
w = np.zeros_like(u)
Expand Down
29 changes: 29 additions & 0 deletions tests/test_interpolation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -156,6 +156,35 @@ def test_spatial_slip_interpolation(field, func, t, z, y, x, expected, mesh):
np.testing.assert_array_almost_equal(velocities, expected)


@pytest.mark.parametrize("mesh", [FlatMesh(), SphericalMesh()])
@pytest.mark.parametrize(
"func, expected",
[
(XPartialslip(), [[0.75], [0.75], [0.5]]),
(XFreeslip(), [[1.0], [1.0], [0.5]]),
],
)
def test_spatial_slip_interpolation_z_face(field, func, expected, mesh):
field.grid.mesh = mesh
field.data[:] = 1.0
field.data[:, 1, 1:3, 1:3] = 0.0 # Set zero land value on the lower Z face

U = field
V = field
W = field
UVW = VectorField("UVW", U, V, W, interp_method=func)

y = 1.5
velocities = UVW[1, 0.5, y, 1.5]

expected = np.array(expected)
if mesh.is_spherical():
expected[0] = expected[0] / (1852 * 60.0 * np.cos(np.radians(y)))
expected[1] = expected[1] / (1852 * 60.0)

np.testing.assert_array_almost_equal(velocities, expected)


@pytest.mark.parametrize(
"interpolator, t, z, y, x, expected",
[
Expand Down
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