def _create_sample_kernel(self, sample_variables):
"""Create the parcels kernel for sampling fields during advection."""
# make sure the fieldset has C code names assigned, etc.
self.fieldset.check_complete()
# string for the kernel itself
f_str = "def sample_kernel(particle, fieldset, time):\n"
for v in sample_variables:
f_str += f"\tparticle.var_{v} = fieldset.{v}.eval(time, particle.depth, particle.lat, particle.lon, applyConversion=False)\n"
else:
f_str += "\tpass"
# create the kernel
self.sample_kernel = parcels.Kernel(
self.fieldset,
self.particleclass.getPType(),
funcname="sample_kernel",
funcvars=["particle", "fieldset", "time"],
funccode=f_str,
)
def make_meridionally_periodic(self, width=None):
"""Mark the domain as meridionally periodic.
This will add a halo to the northern and southern edges of the
domain, so that they may cross over during advection without
being marked out of bounds. If a particle ends up within the
halo after advection, it is reset to the valid portion of the
domain.
If the domain has already been marked as meridionally periodic,
nothing happens.
Due to the method of resetting particles that end up in the
halo, this is incompatible with curvilinear grids.
Args:
width (Optional[int]): The width of the halo,
defaults to 5 (per parcels). This needs to be less
than half the number of points in the grid in the y
direction. This may need to be adjusted for small
domains, or if particles are still escaping the halo.
Note:
This causes the kernel to be recompiled to add another stage
which resets particles that end up in the halo to the main
domain.
If the kernel has already been recompiled for zonal periodicity,
it is again reset to include periodicity in both
directions.
"""
# the method of resetting particles won't work on a curvilinear grid
if self._curvilinear:
raise Exception("curvilinear grids can not be periodic")
# make sure we can't do this twice
if self._is_meridionally_periodic:
return
# add constants that are accessible within the kernel denoting the
# edges of the halo region
self.fieldset.add_constant("halo_north", self._output_grid.lat[-1])
self.fieldset.add_constant("halo_south", self._output_grid.lat[0])
if width is None:
self.fieldset.add_periodic_halo(meridional=True)
else:
self.fieldset.add_periodic_halo(meridional=True, halosize=width)
# unload the previous kernel, and add the meridionally-periodic kernel
self.kernel.remove_lib()
if self._is_zonally_periodic:
k = _doubly_periodic_BC
else:
k = _meridionally_periodic_BC
periodic_kernel = parcels.Kernel(self.fieldset,
self.particleclass.getPType(), k)
self.kernel = parcels.AdvectionRK4 + periodic_kernel + self.sample_kernel
self._compile(self.kernel)
self._is_meridionally_periodic = True
