##
Ice Particle Habit Shortwave Optical Properties

#### Version 1.0

The shortwave optical properties of ice clouds for a variety of particle
"habits" have been parameterized for use in radiative transfer models. The
different habits are shown below. Click on the data link (above) to access the coefficients of the
parameterization.

A statistical relationship between the optical and microphysical properties of ice clouds with various particle habits
was formulated as

where b_{ext} is the volume extinction
coefficient, *WC* is the ice water content , w is
the single scattering albedo, and *g* is the asymmetry parameter.
The coefficients *a*_{n}, *b*_{n}, and
*c*_{n}, are determined in a least squares sense with nonlinear
regression. A different set of coefficients is obtained for every spectral
band and every habit. The parameterization uses an effective "radius" defined by

where *L* is the maximum dimension of an ice crystal, *V* is the volume of the crystal, *A* is the projected area,
and *n(L)* is a size distribution. The figure below shows the relationship between the effective radius and
maximum dimension for 30 different size distributions.

The asymmetry parameter is commonly used with the Henyey-Greenstein (HG)
function as an approximation to the scattering phase function. The HG
function is defined as

The function represents forward scattering reasonably well but it does not
capture backscattering behavior. This problem can be remedied through the
use of the double Henyey-Greenstein function:

where *g*_{2} can be assigned a negative value to account for a backscattering
peak and *f* is a positive fraction in the range [0,1].

### References

Key, J., P. Yang, B. Baum, and S. Nasiri, 2002, Parameterization of shortwave
ice cloud optical properties for various particle habits, J. Geophys. Res.,
107(D13), 4181, doi:10.1029/2001JD000742.
Electronic (PDF) version as published (copyright
American Geophysical Union)