Version 3: Spectral Ice Cloud Bulk Single-Scattering Property Models

Ice cloud bulk single-scattering property models are now available at individual wavelengths between 0.4 – 3.0 µm at 0.01 µm resolution. However, if you want models over a wider range of wavelengths, we recommend that you pull over the files that include the full phase matrix as these models are provided over the full spectral range from 0.2 µm (UV) to 100 µm (Far-IR) - use link in left column to navigate there.

There are currently 4 sets of models available:

(1) One set of models is based on a general habit mixture (GHM) involving a set of 9 habits: solid/hollow bullet rosettes, solid/hollow columns, plates, droxtals, small/large aggregate of plates, and an aggregate of solid columns. The models are based on the assumption of severely roughened particles.

(2) Another set of models is based a mixture of habits developed to more closely align with those found in deep tropical convection (no droxtals, but more aggregates of plates).

(3) A third set of models is based on a habit mixture developed for more for midlatitude/polar ice clouds (droxtals included but not aggregates of plates).

(4) A fourth set of models is based on a single assumed habit: the aggregate of solid columns (ASC). This habit has the lowest asymmetry parameter at a visible wavelength.

The three habit mixtures are described in Baum et al. (2011), with the full reference at the bottom of this page. The files are in NetCDF format with a single file per wavelength. Properties are a function of effective diameter and include the asymmetry parameter, single-scattering albedo, scattering phase function at 498 angles (also provided), the average ice water content inferred from idealized habits and the microphysical data used to generate the models (provided for general information), and the extinction coefficient (β) divided by the IWC. The scientist who asked me to include this parameter has since retired, but perhaps someone else will find it useful.

Because the particle scattering properties are based on severe surface roughening, the phase functions will be much smoother (e.g., no halos) and the asymmetry parameters will be lower in the shortwave region than those based on smooth-faceted particles. We anticipate that if shortwave channels are used to infer optical thickness and effective radius/diameter, the optical thicknesses based on these roughened particles will be lower and the effective radius/diameter will be larger than if smooth particles are assumed.

The NetCDF files also include the wavelength, the version number of the models (currently at 3.5) and the creation date. The spectral models are combined in a tar file - for access to the compressed (gzip) tar file, click on the "Download Models" button at the top of the page. Each file is about 6 MB. Note that there is a new system in place at SSEC and we now ask that you register before downloading data - all we ask for is your name and email. Since there will be updates in the future, we hope that you will permit us to include you on an email list so that we can send a brief note with what has changed in each subsequent version. So when you register, there will be a box that asks you whether you want to be on an email list - it is voluntary on your part.

We are crafting an article that summarizes the details pertaining to the development of these models, so that is in the works. In the meantime, much of the groundwork for these models is documented in the article below. Note, however, that we are only providing models using a general habit mixture at this point. Models employing only a single habit might be provided in the future depending on funding and time contraints. Also, we will not be supplying additional models specifically for midlatitude or tropical clouds as discussed in this manuscript - the general habit mixture seems to compare well with measured polarized reflectances from POLDER/PARASOL so our focus is on these models at present.

References:

Baum, B. A., P. Yang, A. J. Heymsfield, C. Schmitt, Y. Xie, A. Bansemer, Y.-X. Hu, and Z. Zhang, 2011: Improvements to shortwave bulk scattering and absorption models for the remote sensing of ice clouds. J. Appl. Meteor. Clim., 50, 1037-1056.

Yang, P., L. Bi, B. A. Baum, K.-N. Liou, G. Kattawar, and M. Mishchenko, 2013: Spectrally consistent scattering, absorption, and polarization properties of atmospheric ice crystals at wavelengths from 0.2 µm to 100 µm. J. Atmos. Sci., 70, 330-347.

Note: if you have questions or find problems, please let me know (send email to Bryan Baum) so I can look into the issue. If there is a problem, I want to get it fixed.