improver.precipitation_type.hail_fraction module

Module containing the HailFraction class.

class HailFraction(model_id_attr=None)

Bases: PostProcessingPlugin

Calculates the hail fraction using the maximum vertical updraught, the hail size, the cloud condensation level temperature, the convective cloud top temperature and altitude of the hail to rain phase change.

__init__(model_id_attr=None)

Initialise the class.

Parameters:

model_id_attr (Optional[str]) – Name of the attribute used to identify the source model for blending.

_abc_impl = <_abc_data object>

static _compute_hail_fraction(vertical_updraught, hail_size, cloud_condensation_level, convective_cloud_top, hail_melting_level, orography)

Computation of a hail fraction using the following steps: firstly, the hail fraction is estimated as varying linearly with the maximum vertical updraught so that a maximum vertical updraught of 5 m/s has a hail fraction of 0 whilst a maximum vertical updraught of 50 m/s has a hail fraction of 0.25. These values, including the hail fraction upper bound, are based on expert elicitation. Next, the hail fraction is set to zero if either the cloud condensation level temperature is below -5 Celsius, the convective cloud top temperature is above -15 Celsius or the hail melting level is above orography. As a final check, the hail size is then checked for hail with a size larger than 2 mm. If the hail size is above this limit but the hail fraction is below 0.05, the hail fraction is set to 0.05.

The values chosen are based on expert elicitation with some information from Dennis & Kumjian, 2017.

References

Dennis, E.J., and M.R. Kumjian. 2017. “The Impact of Vertical Wind Shear on Hail Growth in Simulated Supercells.” J. Atmos. Sci. 74 (3): 641-663. doi:https://doi.org/10.1175/JAS-D-16-0066.1.

Return type:

ndarray

Returns:

Hail fraction array.

process(vertical_updraught, hail_size, cloud_condensation_level, convective_cloud_top, hail_melting_level, orography)

Calculates the hail fraction using the maximum vertical updraught, the hail_size, the cloud condensation level temperature, the convective cloud top temperature, the altitude of the hail to rain phase change and the orography.

Parameters:

• vertical_updraught (Cube) – Maximum vertical updraught.

• hail_size (Cube) – Hail size.

• cloud_condensation_level (Cube) – Cloud condensation level temperature.

• convective_cloud_top (Cube) – Convective cloud top.

• hail_melting_level (Cube) – Altitude of the melting of hail to rain.

• orography (Cube) – Altitude of the orography.

Return type:

Cube

Returns:

Hail fraction cube.