Source code for improver.cli.visibility_combine_cloud_base

#!/usr/bin/env python
# (C) Crown Copyright, Met Office. All rights reserved.
#
# This file is part of 'IMPROVER' and is released under the BSD 3-Clause license.
# See LICENSE in the root of the repository for full licensing details.
"""CLI to combine visibility and cloud bases"""

from improver import cli




@cli.clizefy
@cli.with_output
def process(
    *cubes: cli.inputcubelist,
    initial_scaling_value: float,
    first_unscaled_threshold: float,
):
    """Combine the probability of visibility above or below a threshold with the probability of
    cloud base at ground level.

    Before combining with a visibility threshold, the cube of cloud base at ground level is
    multiplied by a scalar. The scalar is determined differently depending on the corresponding
    visibility threshold:

    1) If the threshold is greater than or equal to first_unscaled_threshold then the scaling factor
    is 1.
    2) If the threshold is less than first_unscaled_thresholds then a scaling factor is calculated
    by inputting the threshold into a negative fourth level polynomial. The constants in this curve
    have been defined such that a threshold equal to first_unscaled_threshold gives a scaling factor
    of 1.0 and a threshold of 0m gives a scaling factor equal to initial_scaling_value.

    The maximum probability is then taken of the scaled cloud base at ground level and the
    visibility threshold.

    From experimentation the current best known parameter values for combining visibility with a
    cloud base at ground level of 4.5 oktas of cloud or greater are initial_scaling_value=0.6
    and first_unscaled_threshold=5000.0

    Args:
        cubes (iris.cube.CubeList or list of iris.cube.Cube):
            containing:
                visibility (iris.cube.Cube):
                    Cube of probability of visibility relative to thresholds
                cloud base at ground level (iris.cube.Cube):
                    Cube of probability of cloud base at ground level. This cube should only
                    have spatial dimensions (e.g. spot_index or x,y coordinates).
        initial_scaling_value (float):
            The scaling factor for a visibility threshold of 0m
        first_unscaled_threshold (float):
            The first visibility threshold with a corresponding scaling factor of 1.0.
    Returns:
        iris.cube.Cube:
            Cube of probability of visibility combined with scaled cloud bases
    """

    from improver.visibility.visibility_combine_cloud_base import (
        VisibilityCombineCloudBase,
    )

    return VisibilityCombineCloudBase(initial_scaling_value, first_unscaled_threshold)(
        cubes
    )