Ice Cloud Research Team:
Bryan A. Baum (UW-Madison), Ping Yang and colleagues (Texas A&M), Andrew J. Heymsfield, Carl Schmitt, and Aaron Bansemer (NCAR)
- 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 outcome 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.
As our previous (Version 2) models have percolated through the community, the feedback obtained has been invaluable in our effort to improve the description of single scattering properties for the next generation of models. Earlier generations of bulk scattering models were based entirely on smooth particles, leading to scattering phase functions that had haloes and enhanced backscattering at solar wavelengths. This new generation of models also includes, among other advances, moderately or 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.
As progress is made, access will be provided 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. This time around, the 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
Advances incorporated 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)
- Inclusion of three levels of ice particle surface roughening (smooth, moderately roughened, and severely roughened)
- 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