### 2.3.2.2. Snowpack Optical Properties[¶](#snowpack-optical-properties "Permalink to this headline")

Ice optical properties for the five spectral bands are derived offline and stored in a namelist-defined lookup table for online retrieval (see CLM5.0 User’s Guide). Mie properties are first computed at fine spectral resolution (470 bands), and are then weighted into the five bands applied by CLM according to incident solar flux, \\(I^{\\downarrow } (\\lambda )\\). For example, the broadband mass-extinction cross section (\\(\\bar{\\psi }\\)) over wavelength interval \\(\\lambda \_{1}\\) to \\(\\lambda \_{2}\\) is

(2.3.70)[¶](#equation-3-70 "Permalink to this equation")\\\[\\bar{\\psi }=\\frac{\\int \_{\\lambda \_{1} }^{\\lambda \_{2} }\\psi \\left(\\lambda \\right) I^{\\downarrow } \\left(\\lambda \\right){\\rm d}\\lambda }{\\int \_{\\lambda \_{1} }^{\\lambda \_{2} }I^{\\downarrow } \\left(\\lambda \\right){\\rm d}\\lambda }\\\]

Broadband single-scatter albedo (\\(\\bar{\\omega }\\)) is additionally weighted by the diffuse albedo for a semi-infinite snowpack (\\(\\alpha \_{sno}\\))

(2.3.71)[¶](#equation-3-71 "Permalink to this equation")\\\[\\bar{\\omega }=\\frac{\\int \_{\\lambda \_{1} }^{\\lambda \_{2} }\\omega (\\lambda )I^{\\downarrow } ( \\lambda )\\alpha \_{sno} (\\lambda ){\\rm d}\\lambda }{\\int \_{\\lambda \_{1} }^{\\lambda \_{2} }I^{\\downarrow } ( \\lambda )\\alpha \_{sno} (\\lambda ){\\rm d}\\lambda }\\\]

Inclusion of this additional albedo weight was found to improve accuracy of the five-band albedo solutions (relative to 470-band solutions) because of the strong dependence of optically-thick snowpack albedo on ice grain single-scatter albedo ([Flanner et al. (2007)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#flanneretal2007)). The lookup tables contain optical properties for lognormal distributions of ice particles over the range of effective radii: 30\\(\\mu\\)m \\(< r \_{e} < \\text{1500} \\mu \\text{m}\\), at 1 \\(\\mu\\) m resolution. Single-scatter albedos for the end-members of this size range are listed in [Table 2.3.5](#table-single-scatter-albedo-values-used-for-snowpack-impurities-and-ice).

Optical properties for black carbon are described in [Flanner et al. (2007)](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#flanneretal2007). Single-scatter albedo, mass extinction cross-section, and asymmetry parameter values for all snowpack species, in the five spectral bands used, are listed in [Table 2.3.5](#table-single-scatter-albedo-values-used-for-snowpack-impurities-and-ice), [Table 2.3.6](#table-mass-extinction-values), and [Table 2.3.7](#table-asymmetry-scattering-parameters-used-for-snowpack-impurities-and-ice). These properties were also derived with Mie Theory, using various published sources of indices of refraction and assumptions about particle size distribution. Weighting into the five CLM spectral bands was determined only with incident solar flux, as in equation [(2.3.69)](#equation-3-69).

Table 2.3.5 Single-scatter albedo values used for snowpack impurities and ice[¶](#id11 "Permalink to this table")      
| Species
 | Band 1

 | Band 2

 | Band 3

 | Band 4

 | Band 5

 |
| --- | --- | --- | --- | --- | --- |
| Hydrophilic black carbon

 | 0.516

 | 0.434

 | 0.346

 | 0.276

 | 0.139

 |
| Hydrophobic black carbon

 | 0.288

 | 0.187

 | 0.123

 | 0.089

 | 0.040

 |
| Hydrophilic organic carbon

 | 0.997

 | 0.994

 | 0.990

 | 0.987

 | 0.951

 |
| Hydrophobic organic carbon

 | 0.963

 | 0.921

 | 0.860

 | 0.814

 | 0.744

 |
| Dust 1

 | 0.979

 | 0.994

 | 0.993

 | 0.993

 | 0.953

 |
| Dust 2

 | 0.944

 | 0.984

 | 0.989

 | 0.992

 | 0.983

 |
| Dust 3

 | 0.904

 | 0.965

 | 0.969

 | 0.973

 | 0.978

 |
| Dust 4

 | 0.850

 | 0.940

 | 0.948

 | 0.953

 | 0.955

 |
| Ice (\\(r \_{e}\\) = 30 \\(\\mu\\) m)

 | 0.9999

 | 0.9999

 | 0.9992

 | 0.9938

 | 0.9413

 |
| Ice (\\(r \_{e}\\) = 1500 \\(\\mu\\) m)

 | 0.9998

 | 0.9960

 | 0.9680

 | 0.8730

 | 0.5500

 |

Table 2.3.6 Mass extinction values (m2 kg\-1) used for snowpack impurities and ice[¶](#id12 "Permalink to this table")      
| Species
 | Band 1

 | Band 2

 | Band 3

 | Band 4

 | Band 5

 |
| --- | --- | --- | --- | --- | --- |
| Hydrophilic black carbon

 | 25369

 | 12520

 | 7739

 | 5744

 | 3527

 |
| Hydrophobic black carbon

 | 11398

 | 5923

 | 4040

 | 3262

 | 2224

 |
| Hydrophilic organic carbon

 | 37774

 | 22112

 | 14719

 | 10940

 | 5441

 |
| Hydrophobic organic carbon

 | 3289

 | 1486

 | 872

 | 606

 | 248

 |
| Dust 1

 | 2687

 | 2420

 | 1628

 | 1138

 | 466

 |
| Dust 2

 | 841

 | 987

 | 1184

 | 1267

 | 993

 |
| Dust 3

 | 388

 | 419

 | 400

 | 397

 | 503

 |
| Dust 4

 | 197

 | 203

 | 208

 | 205

 | 229

 |
| Ice (\\(r \_{e}\\) = 30 \\(\\mu\\) m)

 | 55.7

 | 56.1

 | 56.3

 | 56.6

 | 57.3

 |
| Ice (\\(r \_{e}\\) = 1500 \\(\\mu\\) m)

 | 1.09

 | 1.09

 | 1.09

 | 1.09

 | 1.1

 |

Table 2.3.7 Asymmetry scattering parameters used for snowpack impurities and ice.[¶](#id13 "Permalink to this table")      
| Species
 | Band 1

 | Band 2

 | Band 3

 | Band 4

 | Band 5

 |
| --- | --- | --- | --- | --- | --- |
| Hydrophilic black carbon

 | 0.52

 | 0.34

 | 0.24

 | 0.19

 | 0.10

 |
| Hydrophobic black carbon

 | 0.35

 | 0.21

 | 0.15

 | 0.11

 | 0.06

 |
| Hydrophilic organic carbon

 | 0.77

 | 0.75

 | 0.72

 | 0.70

 | 0.64

 |
| Hydrophobic organic carbon

 | 0.62

 | 0.57

 | 0.54

 | 0.51

 | 0.44

 |
| Dust 1

 | 0.69

 | 0.72

 | 0.67

 | 0.61

 | 0.44

 |
| Dust 2

 | 0.70

 | 0.65

 | 0.70

 | 0.72

 | 0.70

 |
| Dust 3

 | 0.79

 | 0.75

 | 0.68

 | 0.63

 | 0.67

 |
| Dust 4

 | 0.83

 | 0.79

 | 0.77

 | 0.76

 | 0.73

 |
| Ice (\\(r \_{e}\\) = 30\\(\\mu\\)m)

 | 0.88

 | 0.88

 | 0.88

 | 0.88

 | 0.90

 |
| Ice (\\(r \_{e}\\) = 1500\\(\\mu\\)m)

 | 0.89

 | 0.90

 | 0.90

 | 0.92

 | 0.97

 |

