pyradtran.clouds.CloudGenerator

pyradtran.clouds.CloudGenerator#

class pyradtran.clouds.CloudGenerator[source]#

Bases: object

Factory for CloudLayer sequences.

All methods are static — no instantiation needed. Choose a source method according to your input data:

See also

CloudFileWriter

Persist layers to libRadtran .dat files.

static from_era5_dataset(ds: Dataset, time: datetime | None = None, lat: float | None = None, lon: float | None = None, cloud_variables: Dict[str, str] | None = None, altitude_levels_km: ndarray | None = None, lwc_threshold: float = 1e-06, iwc_threshold: float = 1e-06, default_r_eff_water: float = 10.0, default_r_eff_ice: float = 30.0, pressure_levels: str | None = None, geopotential_var: str | None = None) → List[CloudLayer][source]#

Extract cloud layers from an ERA5 xarray.Dataset.

The method selects a single profile (time, lat, lon), converts LWC / IWC from kg kg⁻¹ to g m⁻³, and returns one CloudLayer per model level that exceeds the water- content thresholds.

Parameters:

  • ds (xarray.Dataset) – ERA5 dataset containing, at minimum, cloud water content on pressure levels.

  • time (datetime, optional) – Time step to select. Defaults to the first available.

  • lat (float, optional) – Coordinates for nearest-neighbour selection. If either is None the spatial mean is used.

  • lon (float, optional) – Coordinates for nearest-neighbour selection. If either is None the spatial mean is used.

  • cloud_variables (dict of str, optional) – Mapping {'lwc': 'clwc', 'iwc': 'ciwc', 'cc': 'cc', 'temp': 't', 'z': 'z'} that connects internal keys to dataset variable names.

  • altitude_levels_km (numpy.ndarray, optional) – Pre-computed altitude grid. When None, altitudes are derived from geopotential height or the hypsometric equation.

  • lwc_threshold (float, default 1e-6) – Minimum liquid water content (g m⁻³) to retain.

  • iwc_threshold (float, default 1e-6) – Minimum ice water content (g m⁻³) to retain.

  • default_r_eff_water (float, default 10.0) – Effective radius for liquid droplets (µm).

  • default_r_eff_ice (float, default 30.0) – Effective radius for ice crystals (µm).

  • pressure_levels (str, optional) – Name of the pressure coordinate. Auto-detected when None.

  • geopotential_var (str, optional) – Name of the geopotential variable. Auto-detected when None.

Returns:

One layer per model level with significant cloud content, sorted from lowest to highest altitude.

Return type:

list of CloudLayer

Raises:

  • ValueError – If no pressure coordinate can be found.

  • KeyError – If a required cloud variable is missing from ds.

Examples

>>> import xarray as xr
>>> ds = xr.open_dataset("era5_cloud.nc")
>>> layers = CloudGenerator.from_era5_dataset(
...     ds, lat=78.0, lon=15.0, default_r_eff_water=8.0
... )

See also

generate_cloud_file_from_era5

One-step convenience wrapper.

static from_simple_parameters(z_base_km: float, z_top_km: float, lwc_g_m3: float = 0.1, iwc_g_m3: float = 0.0, r_eff_um: float = 10.0, cloud_fraction: float = 1.0, n_layers: int = 1) → List[CloudLayer][source]#

Create uniform cloud layers from basic parameters.

The altitude range z_base_km … z_top_km is split into n_layers sub-layers, each receiving the same microphysical values.

Parameters:

  • z_base_km (float) – Cloud base altitude (km above sea level).

  • z_top_km (float) – Cloud top altitude (km above sea level).

  • lwc_g_m3 (float, default 0.1) – Liquid water content (g m⁻³).

  • iwc_g_m3 (float, default 0.0) – Ice water content (g m⁻³).

  • r_eff_um (float, default 10.0) – Effective droplet / crystal radius (µm).

  • cloud_fraction (float, default 1.0) – Cloud fraction (0–1).

  • n_layers (int, default 1) – Number of sub-layers to create.

Returns:

Layers ordered from bottom to top.

Return type:

list of CloudLayer

Raises:

ValueError – If n_layers < 1 or z_base_km >= z_top_km.

Examples

>>> layers = CloudGenerator.from_simple_parameters(
...     z_base_km=1.0, z_top_km=2.0, lwc_g_m3=0.3, n_layers=5
... )
>>> len(layers)
5

See also

CloudFileWriter.write_water_cloud_file

Write layers to disk.

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