Ice Cloud Bulk Scattering Models in the Mid-Wave IR to Far IR spectral region

The models provided through this web page are intended for use in the retrieval of ice cloud properties in the mid-wave infrared (MWIR), infrared (IR), and far infrared (Far IR) spectral regions. The models are provided at 1 cm-1 spectral resolution and span the spectral range from 100 cm-1 to 3250 cm-1. The MWIR spans wavenumbers from about 2000 cm-1 to 3250 cm-1. The IR spans wavenumbers from about 660 cm-1 to 2000 cm-1, and the Far IR spans from 100 cm-1 to 660 cm-1. We provide bulk microphysical and optical properties such as ice water content (IWC), median mass diameter, extinction efficiency, asymmetry factor, and single scattering albedo.

The spectral coverage encompasses measurements made from aircraft interferometers such as the S-HIS and NAST-I, ground-based interferometers such as the AERI, and satellite instruments such as AIRS and IASI. New instruments are being developed to take measurements in the Far IR.

The bulk scattering models are the result of a multiyear team effort to derive new ice cloud scattering models based on reanalysis of in-situ data from a variety of midlatitude and tropical ice cloud field experiments. Here are a few details about the models:

  1. Size distributions are based on 45 size bins (particle size ranges from 2 to 9500 microns).
  2. Ice particle habit distributions vary as a function of maximum dimension.
  3. New ice crystal scattering property libraries have been calculated for a variety of habits, including droxtals, plates, hollow and solid columns, 3-D bullet rosettes, and aggregates.
  4. Each model contains the mean and standard deviation of each microphysical and optical property, including ice water content, mean mass diameter, single scatter albedo, asymmetry factor, extinction efficiency, and the scattering phase function in selected wavenumber regions.

In situ Microphysical Ice Cloud Data

More complete descriptions of the in situ data are provided in the following links.

Description of the field experiments and data sources

Particle size distributions


Ice crystal habit "recipe" implemented for these models

The percentage of each habit used in the integration of a given property over a particle size distribution is based on the particle's maximum dimension.

D < 60 microns:
100% droxtals

60 microns < D < 1000 microns:
15% 3D bullet rosettes
50% solid columns
35% plates

1000 microns < D < 2500 microns:
45% hollow columns
45% solid columns
10% aggregates

2500 microns < D < 9500 microns
97% 3D bullet rosettes
3% aggregates


MWIR - IR - FarIR Spectral Models:

A set of 18 tar files have been prepared, each one specific to a given effective diameter (De). The De span a range from 10 to 180 microns in increments of 10 microns. The habit mixture as described above is used for all calculations of microphysical and optical properties using the idealized ice particles for which we have theoretical scattering calculations.

Each of these files contains the following properties.

Microphysical properties provided once per file as they are not wavenumber dependent:

  • De
  • Ice Water Content (IWC)
  • Total ice particle projected area
  • Total ice particle volume
  • Median mass diameter

Mean and standard deviation of optical properties for each wavenumber between 100 cm-1 and 3250 cm-1: The spectral resolution is 1 cm-1.

  • Asymmetry factor (g)
  • Single scattering albedo (omega)
  • Extinction efficiency (Qe)
  • Scattering cross section (sig_scat)
  • Extinction cross section (sig_ext)

Note: the files provided above do NOT contain scattering phase functions (both means and standard deviations). The scattering phase files are provided in a tar file through the link below; a file is available for each individual wavelength within the tar file. These tar files have been compressed using the gzip utility.

At the present time, phase functions (as a function of De) are available for specific window regions as noted below. A complete set of phase functions for every wavenumber will soon be made available for completeness, although it is unlikely that one would actually see an ice cloud from a spaceborne instrument at highly absorbing wavenumbers.

Scattering Phase Functions from 400-600 cm-1

Scattering Phase Functions from 800-980 cm-1

Scattering Phase Functions from 1100-1250 cm-1

Scattering Phase Functions from 2400-2900 cm-1

All Scattering Phase Functions from 100-3250 cm-1


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