Ice Cloud Research Team: 

Bryan A. Baum (Science and Technology Corporation - Madison, WI),
Ping Yang and colleagues (Texas A&M, College Station, TX),
Andrew J. Heymsfield, Carl Schmitt, and Aaron Bansemer (NCAR, Boulder, CO
)

Goals
  • Improve consistency in ice cloud optical thickness/particle size retrievals from different satellite sensors by developing ice cloud bulk scattering models consistently from ultraviolet through far-infrared wavelengths,
  • Develop the most up-to-date set of individual ice particle single scattering properties for a variety of habits, including droxtals, plates, hollow and solid columns, hollow and solid bullet rosettes, aggregrates of columns, and small/large aggregates of plates (9 habits in all), and
  • Incorporate the best available in-situ microphysical data in the development of bulk scattering models.

The goal of this work is to provide state-of-the-art ice cloud scattering and absorption models for use with various remote sensing instruments, including lidars, satellite imagers, sounders, and interferometers. These scattering models are built consistently using the same microphysical data and development methodology. This generation of models incorporates severely roughened particles.

At solar wavelengths, use of roughened particles reduces the maxima (e.g., halos) at forward scattering angles and smoothes the phase function at backscattering angles, resulting in a decrease in the asymmetry parameter.

Access is available to spectral models (i.e., models developed at a single wavelength) and narrowband models in which the properties are integrated over a spectral response function. All models are formatted in netCDF.

A summary of pertinent improvements is listed below.

Advances in the microphysical data:
  • Increase of individual particle size distributions (PSDs) to more than 14,000 (and counting) from 1117 PSDs used in earlier models
  • Range of IWC values now covers 6 orders of magnitude, up from 3 orders of magnitude in earlier models
  • Re-analysis of historical microphysical data to mitigate influence of potential particle shattering at inlet of particle probes on the resulting PSDs
  • Data from new probes (CAPS, SID-3)
  • More sensible prescription of habit as a function of particle size developed for new models
  • Microphysical data are now available on this site
Advances in the single scattering calculations:
  • Models are now available from the UV through the IR with no spectral gaps.
  • Calculations are performed using the updated ice index of refraction reported in Warren and Brandt (JGR, 2008)
  • Use of severely roughened ice particles
  • Improvements in light scattering calculations (e.g., new treatment of forward scattering resulting in removal of delta transmission energy term)
  • Smooth transition of the extinction/absorption efficiencies across the wavelength spectrum
  • Single scattering properties now provided for the full phase matrix (i.e., polarization adds a new and very important dimension)
  • Adoption of three new habits: hollow bullet rosettes, small and large aggregates of plates