COP: Cirrus Optical Properties

• COP is available by ftp.
• If you are only interested in recent changes and comments, look at the NEWS page.

1. DATA FILES

There are two kinds of data files. The first one contains the phasefunctions and the parts of the phasefunctions polarized parallel and perpendicular to the scattering plane. The second one contains tables of the most important optical properties in dependence of wavelength and particle size and shape.

1. COP contains phasefunctions of 6 hexagonal plates in the size range between 20 µm and 2000 µm and of 8 columns between 2 µm and 2000 µm. The particles are oriented randomly in space. There are calculations for 31 wavelengths from 0.28 µm to 10. µm and the data are stored correspondingly in 31 files named for example "0355_R" with 0355 meaning a wavelength of 0.355 µm and "R" representing randomly oriented particles (0001 represents the 10. µm wavelength). Each file contains the phasefunctions of all 14 ice crystals. These phase functions are normalized to 1.
2. Additionally 7 tables with extinction coefficients, single scattering albedo, asymmetry parameter, and lidarratio of the backscattered signal for 6 wavelengths and horizontally oriented ice crystals are provided. The corresponding file names are for example "COPTAB15" for a solar elevation angle of 15 degrees. "COPTABR" contains the values for randomly oriented particles.

In these files the particle sizes A and C are given in [µm], the extinction coefficients in [µm*µm] (i.e. as extinction cross sections) and the lidarratio in [sr].

As an example, you may have a look at the

• phasefunctions of a columnar ice crystal at different wavelengths
  
• phasefunctions of columnar ice crystals of different size at 1615 nm.
  
• phasefunctions of platelike ice crystals of different size at 550 nm.
• single scattering albedo of all ice crystals at all wavelengths
  
• asymmetry parameters of all ice crystals at all wavelengths

for particles randomly oriented in space, and at

• single scattering albedo at 1615 nm for different solar elevation angles
  
• asymmetry parameter at 1615 nm for different solar elevation angles

for particles oriented in a horizontal plane.

In addition, there is a

• table of the geometrical dimensions of the columns and plates.

2. PROGRAM

There is a program "COP.FOR", written in standard FORTRAN77 (hopefully), to allow the calculation of 'Cirrus Optical Properties', i.e., size distribution wheighted phasefunctions and other optical properties from the optical properties of the single particles. The program asks for all the input it needs. First you have to select a wavelength. Second you must decide which size distribution you want to use. There are three possibilities:

1. you may use predefined size distributions after Heymsfield and Platt (1984) (J. Atm. Sci., 41, 846-855). If you decide to do so, you are asked to choose one of the 8 possibilities, corresponding to 8 different temperature ranges.
2. you may interactively introduce own values of number densities for the indicated radius intervals.
3. you may write your number densities (in particles / m**3) to the file "NUMIN" from which the program will read them. An example of NUMIN is provided.

After this you have to choose a mixing ratio of columnar and platelike crystals. The program will write its results to the file "RESULTS". Note that the extinction coefficients now are volume extinction coefficients given in [1/m] and are valid for 1 [particle/cm**3]. To get the total value, you have to multiply this with the actual particle number density which is also given.

3. ADDITIONAL DATA ON REQUEST

The extent of our calculations is much larger than what is presented here. If you are interested, we could expand COP by the following data:

• azimuthally integrated phasefunctions of horizontally oriented particles.

In addition, phasefunctions of horizontally oriented crystals which depend on the scattering azimuth angle can be provided on request. They cannot be presented in this data base because of restrictions in storage capacity.

In some single exceptions it may be possible to calculate special cases on request.

4. FUTURE PLANS

We plan to extend the COPE package with calculations for imperfect hexagonal crystals at lidar wavelengths.

5. AVAILABILITY

COP is available by anonymous ftp at ftp.lrz-muenchen.de in the directory "pub/science/meteorology/cirrus".

6. Contact

We are very curious to learn what you are using COP for. Please send us a short note about that.

If you did find this database by accident (not following the note in our paper) and think it may be useful for you, please send us a short note.