def apply_ice(self, prob_lightning_cube, ice_cube):
"""
Modify Nowcast of lightning probability with ice data from a radar
composite (VII; Vertically Integrated Ice)
Args:
prob_lightning_cube (iris.cube.Cube):
First-guess lightning probability.
The forecast_period coord is modified in-place to "minutes".
ice_cube (iris.cube.Cube):
Analysis of vertically integrated ice (VII) from radar
thresholded at self.ice_thresholds.
Units of threshold coord modified in-place to kg m^-2
Returns:
iris.cube.Cube:
Output cube containing updated nowcast lightning probability.
This cube will have the same dimensions and meta-data as
prob_lightning_cube.
The influence of the data in ice_cube reduces linearly to zero
as forecast_period increases to 2H30M.
Raises:
iris.exceptions.ConstraintMismatchError:
If ice_cube does not contain the expected thresholds.
"""
prob_lightning_cube.coord("forecast_period").convert_units("minutes")
# check prob-ice threshold units are as expected
ice_threshold_coord = find_threshold_coordinate(ice_cube)
ice_threshold_coord.convert_units("kg m^-2")
new_cube_list = iris.cube.CubeList([])
err_string = "No matching prob(Ice) cube for threshold {}"
for cube_slice in prob_lightning_cube.slices_over("time"):
fcmins = cube_slice.coord("forecast_period").points[0]
for threshold, prob_max in zip(self.ice_thresholds,
self.ice_scaling):
ice_slice = ice_cube.extract(
iris.Constraint(coord_values={
ice_threshold_coord:
lambda t: isclose(t.point, threshold)
}))
if not isinstance(ice_slice, iris.cube.Cube):
raise ConstraintMismatchError(err_string.format(threshold))
# Linearly reduce impact of ice as fcmins increases to 2H30M.
ice_scaling = [0.0, (prob_max * (1.0 - (fcmins / 150.0)))]
if ice_scaling[1] > 0:
cube_slice.data = np.maximum(
rescale(
ice_slice.data,
data_range=(0.0, 1.0),
scale_range=ice_scaling,
clip=True,
),
cube_slice.data,
)
new_cube_list.append(cube_slice)
new_cube = new_cube_list.merge_cube()
new_cube = check_cube_coordinates(prob_lightning_cube, new_cube)
return new_cube
def process(self, cubelist):
"""
Produce Nowcast of lightning probability.
Args:
cubelist (iris.cube.CubeList):
Where thresholds are listed, only these threshold values will
be used.
Contains cubes of
* First-guess lightning probability
* Nowcast precipitation probability
(required thresholds: > 0.5, 7., 35. mm hr-1)
* Nowcast lightning rate
* (optional) Analysis of vertically integrated ice (VII)
from radar thresholded into probability slices
at self.ice_thresholds.
Returns:
iris.cube.Cube:
Output cube containing Nowcast lightning probability.
This cube will have the same dimensions as the input
Nowcast precipitation probability after the threshold coord
has been removed.
Raises:
iris.exceptions.ConstraintMismatchError:
If cubelist does not contain the expected cubes.
"""
first_guess_lightning_cube = cubelist.extract(
"probability_of_rate_of_lightning_above_threshold", strict=True)
lightning_rate_cube = cubelist.extract(
"rate_of_lightning", strict=True)
lightning_rate_cube.convert_units("min^-1") # Ensure units are correct
prob_precip_cube = cubelist.extract(
"probability_of_lwe_precipitation_rate_above_threshold",
strict=True)
# Now find prob_vii_cube. Can't use strict=True here as cube may not be
# present, so will use a normal extract and then merge_cube if needed.
prob_vii_cube = cubelist.extract(
"probability_of_vertical_integral_of_ice_above_threshold")
if prob_vii_cube:
prob_vii_cube = prob_vii_cube.merge_cube()
precip_threshold_coord = find_threshold_coordinate(prob_precip_cube)
precip_threshold_coord.convert_units('mm hr-1')
precip_slice = prob_precip_cube.extract(
iris.Constraint(coord_values={
precip_threshold_coord: lambda t: isclose(t.point, 0.5)}))
if not isinstance(precip_slice, iris.cube.Cube):
raise ConstraintMismatchError(
"Cannot find prob(precip > 0.5 mm hr-1) cube in cubelist.")
template_cube = self._update_metadata(precip_slice)
new_cube = self._modify_first_guess(
template_cube, first_guess_lightning_cube, lightning_rate_cube,
prob_precip_cube, prob_vii_cube)
# Adjust data so that lightning probability does not decrease too
# rapidly with distance.
self.neighbourhood.process(new_cube)
return new_cube
def apply_precip(self, prob_lightning_cube: Cube,
prob_precip_cube: Cube) -> Cube:
"""
Modify Nowcast of lightning probability with precipitation rate
probabilities at thresholds of 0.5, 7 and 35 mm/h.
Args:
prob_lightning_cube:
First-guess lightning probability.
prob_precip_cube:
Nowcast precipitation probability
(threshold > 0.5, 7., 35. mm hr-1)
Units of threshold coord modified in-place to mm hr-1
Returns:
Output cube containing updated nowcast lightning probability.
This cube will have the same dimensions and meta-data as
prob_lightning_cube.
Raises:
iris.exceptions.ConstraintMismatchError:
If prob_precip_cube does not contain the expected thresholds.
"""
new_cube_list = iris.cube.CubeList([])
# check prob-precip threshold units are as expected
precip_threshold_coord = find_threshold_coordinate(prob_precip_cube)
precip_threshold_coord.convert_units("mm hr-1")
# extract precipitation probabilities at required thresholds
for cube_slice in prob_lightning_cube.slices_over("time"):
this_time = iris_time_to_datetime(
cube_slice.coord("time").copy())[0]
this_precip = prob_precip_cube.extract(
iris.Constraint(time=this_time)
& iris.Constraint(coord_values={
precip_threshold_coord:
lambda t: isclose(t.point, 0.5)
}))
high_precip = prob_precip_cube.extract(
iris.Constraint(time=this_time)
& iris.Constraint(coord_values={
precip_threshold_coord:
lambda t: isclose(t.point, 7.0)
}))
torr_precip = prob_precip_cube.extract(
iris.Constraint(time=this_time)
& iris.Constraint(coord_values={
precip_threshold_coord:
lambda t: isclose(t.point, 35.0)
}))
err_string = "No matching {} cube for {}"
if not isinstance(this_precip, iris.cube.Cube):
raise ConstraintMismatchError(
err_string.format("any precip", this_time))
if not isinstance(high_precip, iris.cube.Cube):
raise ConstraintMismatchError(
err_string.format("high precip", this_time))
if not isinstance(torr_precip, iris.cube.Cube):
raise ConstraintMismatchError(
err_string.format("intense precip", this_time))
# Increase prob(lightning) to Risk 2 (pl_dict[2]) when
# prob(precip > 7mm/hr) > phighthresh
cube_slice.data = np.where(
(high_precip.data >= self.phighthresh)
& (cube_slice.data < self.pl_dict[2]),
self.pl_dict[2],
cube_slice.data,
)
# Increase prob(lightning) to Risk 1 (pl_dict[1]) when
# prob(precip > 35mm/hr) > ptorrthresh
cube_slice.data = np.where(
(torr_precip.data >= self.ptorrthresh)
& (cube_slice.data < self.pl_dict[1]),
self.pl_dict[1],
cube_slice.data,
)
# Decrease prob(lightning) where prob(precip > 0.5 mm hr-1) is low.
cube_slice.data = apply_double_scaling(this_precip, cube_slice,
self.precipthr,
self.ltngthr)
new_cube_list.append(cube_slice)
new_cube = new_cube_list.merge_cube()
new_cube = check_cube_coordinates(prob_lightning_cube, new_cube)
return new_cube
def _modify_first_guess(
self,
cube: Cube,
first_guess_lightning_cube: Cube,
lightning_rate_cube: Cube,
prob_precip_cube: Cube,
prob_vii_cube: Optional[Cube] = None,
) -> Cube:
"""
Modify first-guess lightning probability with nowcast data.
Args:
cube:
Provides the meta-data for the Nowcast lightning probability
output cube.
first_guess_lightning_cube:
First-guess lightning probability.
Must have same x & y dimensions as cube.
Time dimension should overlap that of cube (closest slice in
time is used with a maximum time mismatch of 2 hours).
This is included to allow this cube to come from a different
modelling system, such as the UM.
lightning_rate_cube:
Nowcast lightning rate.
Must have same dimensions as cube.
prob_precip_cube:
Nowcast precipitation probability (threshold > 0.5, 7, 35).
Must have same other dimensions as cube.
prob_vii_cube:
Radar-derived vertically integrated ice content (VII).
Must have same x and y dimensions as cube.
Time should be a scalar coordinate.
Must have a threshold coordinate with points matching.
self.vii_thresholds.
Can be <No cube> or None or anything that evaluates to False.
Returns:
Output cube containing Nowcast lightning probability.
Raises:
iris.exceptions.ConstraintMismatchError:
If lightning_rate_cube or first_guess_lightning_cube do not
contain the expected times.
"""
new_cube_list = iris.cube.CubeList([])
# Loop over required forecast validity times
for cube_slice in cube.slices_over("time"):
this_time = iris_time_to_datetime(
cube_slice.coord("time").copy())[0]
lightning_rate_slice = lightning_rate_cube.extract(
iris.Constraint(time=this_time))
err_string = "No matching {} cube for {}"
if not isinstance(lightning_rate_slice, iris.cube.Cube):
raise ConstraintMismatchError(
err_string.format("lightning", this_time))
first_guess_slice = extract_nearest_time_point(
first_guess_lightning_cube,
this_time,
allowed_dt_difference=7201)
first_guess_slice = cube_slice.copy(data=first_guess_slice.data)
first_guess_slice.coord("forecast_period").convert_units("minutes")
fcmins = first_guess_slice.coord("forecast_period").points[0]
# Increase prob(lightning) to Risk 2 (pl_dict[2]) when
# lightning nearby (lrt_lev2)
# (and leave unchanged when condition is not met):
first_guess_slice.data = np.where(
(lightning_rate_slice.data >= self.lrt_lev2)
& (first_guess_slice.data < self.pl_dict[2]),
self.pl_dict[2],
first_guess_slice.data,
)
# Increase prob(lightning) to Risk 1 (pl_dict[1]) when within
# lightning storm (lrt_lev1):
# (and leave unchanged when condition is not met):
lratethresh = self.lrt_lev1(fcmins)
first_guess_slice.data = np.where(
(lightning_rate_slice.data >= lratethresh)
& (first_guess_slice.data < self.pl_dict[1]),
self.pl_dict[1],
first_guess_slice.data,
)
new_cube_list.append(first_guess_slice)
new_prob_lightning_cube = new_cube_list.merge_cube()
new_prob_lightning_cube = check_cube_coordinates(
cube, new_prob_lightning_cube)
# Apply precipitation adjustments.
new_prob_lightning_cube = self.apply_precip(new_prob_lightning_cube,
prob_precip_cube)
# If we have VII data, increase prob(lightning) accordingly.
if prob_vii_cube:
new_prob_lightning_cube = self.apply_ice(new_prob_lightning_cube,
prob_vii_cube)
return new_prob_lightning_cube
