improver.cli.visibility_combine_cloud_base module
CLI to combine visibility and cloud bases
- process(*cubes, initial_scaling_value, first_unscaled_threshold)[source]
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
- Parameters:
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:
Cube of probability of visibility combined with scaled cloud bases
- Return type: