Input Parameters

BioSNICAR is configured through run_model() keyword arguments or the inputs.yaml file. This page documents every parameter.

Illumination

Parameter	Key	Type	Default	Description
Solar zenith angle	`solzen`	int	50	Degrees from vertical (1–89). Higher = more oblique.
Direct/diffuse	`direct`	int	1	1 = clear sky (direct beam), 0 = overcast (diffuse).
Incoming spectrum	`incoming`	int	0	Index 0–6 selecting atmospheric irradiance profile. Set in `inputs.yaml`.

The incoming parameter selects from pre-computed irradiance spectra representing different atmospheric conditions. It is a discrete index and cannot be continuously interpolated.

Ice column structure

Parameter	Key	Type	Default	Description
Layer type	`layer_type`	int or list	0	0 = granular snow, 1 = solid ice with Fresnel, 3 = solid ice without Fresnel
Layer thickness	`dz`	list[float]	[0.02, 0.146]	Thickness of each layer in metres
Grain/bubble radius	`rds`	int or list	500	Effective radius in µm
Density	`rho`	int or list	400	Bulk density in kg/m³
Grain shape	`shp`	int or list	0	0=sphere, 1=spheroid, 2=hex plate, 3=Koch snowflake, 4=hex prism
Grain aspect ratio	`grain_ar`	float or list	1.0	Aspect ratio for non-spherical grains
Liquid water content	`lwc`	float or list	0.0	Fractional liquid water content
Hex side length	`hex_side`	float or list	50	Side length for hexagonal prism grains (µm)
Hex length	`hex_length`	float or list	100	Length for hexagonal prism grains (µm)

How list overrides work

When you pass a list, each element corresponds to a layer. The number of layers is determined by the longest list you pass:

# 5-layer configuration
outputs = run_model(
    dz=[0.02, 0.05, 0.05, 0.05, 0.83],
    rds=[800, 900, 1000, 1100, 1200],
    rho=[500, 600, 700, 750, 800],
)

If a list override changes the number of layers, all per-layer attributes are automatically resized:

Ice properties (rds, rho, grain_ar, etc.) are extended by repeating their last value
Impurity concentrations are zero-padded

This means you only need to specify the parameters you care about.

Scalar overrides

Scalar values for ice parameters are broadcast to all layers. Scalar impurity concentrations are applied to the first layer only:

# rds=1000 applies to all layers; algae only in surface layer
outputs = run_model(rds=1000, glacier_algae=50000)

Impurity concentrations

Parameter	Key	Type	Unit	Description
Black carbon	`black_carbon`	float or list	ppb	Soot from combustion
Snow algae	`snow_algae`	float or list	cells/mL	Sphaerocystis-type algae
Glacier algae	`glacier_algae`	float or list	cells/mL	Ancylonema-type filamentous algae
Mineral dust	`dust`	float or list	ppb	Mineral aerosol

# Scalar: applied to first layer only
run_model(black_carbon=5000, glacier_algae=50000)
 
# Per-layer list
run_model(glacier_algae=[40000, 10000, 0])

Advanced parameters

These parameters are not exposed as run_model() keyword overrides. Change them by editing inputs.yaml directly or passing a custom YAML via input_file=:

run_model(input_file="path/to/custom_inputs.yaml")

Parameter	Location	Description
Refractive index variant	`OP_DIR_STUBS`	Select Warren 1984, Warren 2008, or Picard 2016 ice refractive indices
Surface reflectance file	`SFC`	Fresnel reflectance data for the ice–air interface
RT approximation	`APRX_TYP`	Two-stream approximation variant
CDOM	`cdom`	Coloured dissolved organic matter absorption toggle
Liquid water coating	`water`	Water coating around snow grains

Adding custom impurity types

Obtain an optical property .npz file (containing MAC, SSA, asymmetry parameter arrays)
Add it to the LAP archive (data/OP_data/480band/lap.npz)

Add an entry to inputs.yaml:

IMPURITIES:
  my_new_impurity:
    FILE: "my_impurity_file.npz"
    COATED: False
    UNIT: 0          # 0 = ppb (mass), 1 = cells/mL (count)
    CONC: [0, 0]     # default concentration per layer

Use the YAML key as the parameter name: run_model(my_new_impurity=500)

See the in-line annotations in inputs.yaml for valid values and guidance.

Overview Running the Model