Ice Cloud Bulk Scattering Models for the Visible and InfraRed Scanner (VIRS)

The VIRS imager resides on the TRMM (Tropical Rainfall Measuring Mission) platform. TRMM (pronounced generally as 'trim') is a joint mission between NASA and the Japan Aerospace Exploration Agency (JAXA) designed to monitor and study tropical rainfall.

These 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 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, fraction of delta transmitted energy, extinction efficiency, and the scattering phase function.

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

VIRS Narrowband Models:

A tar file has been prepared for each of the five VIRS bands noted below. Each tar file contains a set of 18 models, with effective diameters (De) spanning a range from 10 to 180 microns in increments of 10 microns.

Naming convention of individual files: The band number and effective diameter is in the file name. For example, a file named VIRS_mix1_b02_d080.dat means this: habit mixture 1 as described above, VIRS band 2 (1.6 micron wavelength), and a De of 80 microns.

Note: Channels 3, 4, and 5 have been updated as of April 10, 2006. These new models incorporate a significant update in scattering libraries detailed in Yang et al. (2005), with the full reference below. These new models tend to have a higher asymmetry factor and a lower single scattering albedo than the previous models. The changes in the scattering phase function are minimal. There is no delta transmission energy in these new models, as this is primarily only important at shorter wavelengths. To make these new models distinguishable from the previous ones that we had available prior to 4/10/2006, the file naming convention has been changed so that prefix 'b' for band is now 'ch' for channel. Thus, a file named VIRS_mix1_ch03_d080.dat means this: habit mixture 1 as described above, VIRS channel 3 (3.75 micron wavelength), and a De of 80 microns.

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