THE DATABASE AND ASSOCIATED SOFTWARE PACKAGE
OPAC (Optical Properties of Aerosols and Clouds)
The software package OPAC (Optical Properties of Aerosols and Clouds) has been developed by Hess and Koepke (Meteorolgisches Institut der Universität München, Germany) and Schult (Max-Plank-Institut für Meteorologie, Hamburg, Germany). A complete description of OPAC is given in Hess et al. (1998) referred to as BAMS98 in the following.
The OPAC archive consists of two parts :
FIRST PART :
This first part of OPAC is a database of microphysical and optical properties of 10 aerosol components (Table 1), 6 water clouds (Table 2a), and 3 ice clouds (Table 2b), both in the solar and terrestrial spectral range: for 61 wavelengths between 0.25 and 40 micrometers for aerosol and water clouds, for 32 wavelengths between 0.28 and 10 micrometers for ice clouds, and for 8 relative humidity conditions (i.e.: 0%, 50%, 70%, 80%, 90%, 95%, 98%, 99%) in the case of those aerosol components that are able to take up water.
The optical properties of aerosols particles and cloud droplets are modeled under the assumption of sphericity (Mie theory; Quenzel and Muller, 1978), those of ice crystals under the assumption of hexagonal columns (Hess and Wiegner, 1994) in the solar spectral range. In the terrestrial spectral range, ice crystals are also considered to be spheres.
Table 1 : Aerosol components used in the OPAC software package (BAMS98)
| Aerosol components | References |
| – Insoluble (soil particles with a certain amount of organic material) – Soot (absorbing black carbon) – Water-soluble (sulfates, nitrates & other water-soluble substances) – Sea salt -acc. Mode (*) (various kinds of saltaltcontained in seawater) – Sea salt -coa. mode (*) (various kinds of salt contained in seawater) – Mineral -nuc. mode (**) (a mixture of quartz and clay minerals) – Mineral -coa. mode (**) (a mixture of quartz and clay minerals) – Mineral -acc. mode (**) (a mixture of quartz and clay minerals) – Mineral-transported (desert dust transported over long distances with a reduced amount of large particles) – Sulfate droplets (75% solution of H2SO4) |
Deepak and Gerber, 1983;
Shettle and Fenn, 1979; Almedia et al., 1991; Koepke et al., 1997 |
Table 2a : Water clouds used in the OPAC software package (BAMS98)
|
Clouds |
References |
| Stratus (continental) (water clouds) | Tampieri and Tomasi 1976; Diem, 1948; Hofmann and Roth, 1989. |
| Stratus (maritime) (water clouds) | Tampieri and Tomasi 1976; Stephens et al., 1978. |
| Cumulus (continental, clean) (water clouds) | Tampieri and Tomasi 1976; Squires 1958; Leatich et al., 1992. |
| Cumulus (continental, polluted) (water clouds) | Tampieri and Tomasi 1976; Diem, 1948; Fitzgerald and Spyers-Duran, 1973. |
| Cumulus (maritime) (water clouds) | Tampieri and Tomasi 1976. |
| Fog | Tampieri and Tomasi 1976. |
Table 2b : Ice clouds used in the OPAC software package (BAMS98)
| Clouds | References |
| Cirrus 1 (T=-25° C) (ice clouds) | Heymsfield and Platt, 1984; Strauss et al., 1997; Hess and Wiegner, 1994. |
| Cirrus 2 (T=-50° C) (ice clouds) | |
| Cirrus 3 (T=-50° C)+ small particles (ice clouds) |
GEISA-2003 OPAC Database Content
The following optical properties of aerosols and clouds have been archived (see, e.g. Van de Hulst, 1981, BAMS98, for explicit formulas and definitions):
- extinction coefficient (km-1)
- scattering coefficient (km-1)
- absorption coefficient (km-1)
- single scattering albedo
- asymmetry parameter
- volume phase function (km-1 sr-1)
Parameters 1 to 4 are archived for 61 wavelengths in case of aerosols and water clouds and for 32 wavelengths in case of ice clouds. Parameter 5 is archived for the same wavelengths and for 167 values of angles.
Tables 3 to 5 detail the database contents
- AEROSOL DATA
σ, rmodN, rmodV, rmin, and rmax, are parameters of the lognormal size distributions. The term ρ is the density of the aerosol particles and M* is the aerosol mass per cubic meter air, integrated over the size distribution and normalized to 1 particle per cubic centimeter of air. The term M* [(μg m-3) (particles cm-3)-1] is calculated with a cutoff radius of 7.5 micrometer.
Table 3 : Microphysical and optical properties of aerosol components in dry state.
| Component | σ | rmodN (μm) |
rmodV (μm) |
rmin (μm) |
rmax (μm) |
ρ (g cm-3) |
M* (μg m-3)/(part. cm-3) |
| Insoluble | 2.51 | 0.471 | 6.00 | 0.005 | 20.0 | 2.0 | 23.7 |
| Water-soluble | 2.24 | 0.0212 | 0.15 | 0.005 | 20.0 | 1.8 | 1.34 10-3 |
| Soot | 2.00 | 0.0118 | 0.05 | 0.005 | 20.0 | 1.0 | 5.99 10-5 |
| Sea salt (acc.mode) | 2.03 | 0.209 | 0.94 | 0.005 | 20.0 | 2.2 | 0.802 |
| Sea salt (coa. Mode) | 2.03 | 1.75 | 7.90 | 0.005 | 60.0 | 2.2 | 224 |
| Mineral (nuc. Mode) | 1.95 | 0.07 | 0.27 | 0.005 | 20.0 | 2.6 | 0.0278 |
| Mineral (acc. Mode) | 2.00 | 0.39 | 1.60 | 0.005 | 20.0 | 2.6 | 5.53 |
| Mineral (coa. Mode) | 2.15 | 1.90 | 11.00 | 0.005 | 60.0 | 2.6 | 324 |
| Mineral-transported | 2.20 | 0.50 | 3.00 | 0.02 | 5.0 | 2.5 | 15.9 |
| Sulfate droplets | 2.03 | 0.0695 | 0.31 | 0.005 | 20.0 | 1.7 | 0.0228 |
- WATER CLOUDS AND FOG
Table 4 : Microphysical and optical properties of the water-cloud and fog models at 61 wavelengths between 0.25 and 40 micrometers.
Values listed in columns 2 to 8 are parameters of the cloud size distribution function. The liquid water content L is listed in column 9.
| Component | rmod (μm) |
α | γ | a | B | reff (μm) |
N (cm-3) |
L (g m-3) |
| Stratus (continental) | 4.7 | 5 | 1.05 | 9.792 10-3 | 0.938 | 7.33 | 250 | 0.28 |
| Stratus (maritime) | 6.75 | 3 | 1.30 | 3.818 10-3 | 0.193 | 11.30 | 80 | 0.30 |
| 0.0782 | 4.8 | 5 | 2.16 | 1.105 10-3 | 5.77 | 400 | 0.26 | |
| Cumulus (cont., polluted) | 3.53 | 8 | 2.15 | 8.118 10-4 | 0.247 | 4.00 | 1300 | 0.30 |
| Cumulus (maritime) | 10.4 | 4 | 2.34 | 5.674 10-5 | 0.00713 | 12.68 | 65 | 0.44 |
| Fog | 8.06 | 4 | 1.77 | 3.041 10-4 | 0.0562 | 10.70 | 15 | 0.058 |
- ICE CLOUDS (CIRRUS)
Table 5 : Microphysical and optical properties of ice cloud model at 32wavelengths between 0.28 and 10 micrometers. Values listed in columns 2 to 9 are parameters of the ice cloud size distribution function. The ice content I is listed in column 10. See BAMS98 for details
| Component | a1 | b1 | a2 | b2 | χ0 | ƒ | reff (μm) |
N (cm-3) |
I (g m-3) |
| Cirrus 1: -25° C | 4.486 x 108 | -2.417 | 1.545 x 1014 | -4.376 | 670 | 0.909 | 91.7 | 0.107 | 0.0260 |
| Cirrus 2: -50° C | 5.352 x 1010 | -3.545 | — | — | — | 3.48 | 57.4 | 0.0225 | 0.00193 |
| Cirrus 3: -50° C (+ small particles) |
5.352 x 1010 | -3.545 | — | — | — | 3.48 | 34.3 | 0.578 | 0.00208 |
SECOND PART: OPAC FORTRAN PROGRAM
The OPAC FORTRAN program allows the user to extract data from the dataset and to calculate additional optical properties of mixtures of the stored clouds and aerosol components.
For a user-defined atmospheric mixture, the following optical properties can be computed (BAMS98):
- extinction coefficient (km-1),
- scattering coefficient (km-1),
- absorption coefficient (km-1),
- volume phase function (km-1 sr-1),
- single scattering albedo,
- asymmetry parameter,
- aerosol optical depth,
- spectral turbidity factor,
- lidar ratio,
- mass extinction cross section,
- mass absorption cross section,
- normalized extinction coefficient ,
- spectrally weighted coefficients ,
- Angstrom coefficients ,
- visibity ,
- refractive index .
REFERENCES
d’Almedia, G.A., P. Koepke, and E.P. Shettle, “Atmospheric Aerosols: Global Climatology and Radiative Characteristics”, A. Deepak Publishing, 561 pp. (1991)
Deepak, A., and H. E. Gerber, Eds., “Report of the experts meeting on aerosols and their climatic effects”, WCP-55, 107 pp. [Available from World Meteorological Organization, Case Postale No. 5, CH-1211 Geneva, Switzerland.] (1983)
Diem, M., “Messungen der grösse von wolkenelementen II”, Meteor. Rundsch., 1, 261–273 (1948)
Fitzgerald, J. W., and P. A. Spyers-Duran, “Changes in cloud nucleus concentration and cloud droplet size distribution associated with pollution from St. Louis”, J. Appl. Meteor., 12, 511–516 (1973)
Hess M., and M. Wiegner, “COP: A data library of optical properties of hexagonal ice crystals”, Appl. Optics, 33, 7740-7746 (1994)
Hess M., P. Koepke, and I. Schult, “Optical properties of Aerosols and Clouds: The software package OPAC”, Bulletin of American Meteorological Society, 79, 831-844 (1998)
Heymsfield, A. J., and C. M. R. Platt, “A parameterization of the particle size spectrum of ice clouds in terms of the ambient temperature and the ice water content”, J. Atmos. Sci., 41, 846–855 (1984)
Hoffmann, H.-E., and R. Roth, “Cloud physical parameters in dependence on height above cloud base in different clouds”, Meteor. Atmos. Phys., 41, 247–254 (1989)
Koepke P., M. Hess, I. Schult, and E.P. Shettle, “Global aerosol dataset”, Report N 243, Max-Plank-Institut für Meteorologie, Hamburg, 44 pp., September 1997
Leaitch, W. R., G. A. Isaac, J. W. Strapp, C. M. Banie, and H. A. Wiebe, “The relationship between cloud droplet number concentrations and anthropogenic pollution: Observations and climatic implications”, J. Geophys. Res., 97 (D2), 2463–2474 (1992)
Quenzel H., and H. Müller, “Optical properties of single Mie particles: Diagrams of intensity-, extinction-, scattering-, and absorption efficiencies”, Universität München, Meteorologisches Institut, Wiss. Mit., 34, 59 pp. (1978)
Shettle, E. P. and Fenn, R. W., “Models for the Aerosols of the Lower Atmosphere and the Effects of Humidity Variations on Their Optical Properties”, AFGL-TR-79-0214, 20 Sept 1979, ADA085951.
Squires, P., “The microstructure and colloidal stability of warm clouds”, Tellus, 10, 256–261 (1958)
Stephens, G. L., C. W. Paltridge, and C. M. R. Platt, “Radiation profiles in extended water clouds III: Observations”, J. Atmos. Sci., 35, 2133–2141 (1978)
Strauss, B., R. Meerkoetter, B. Wissinger, P. Wendling, and M. Hess, “On the regional climatic impact of contrails: Microphysical and radiative properties of contrails and natural cirrus clouds”, Ann. Geophys., 15, 1457–1467 (1997)
Tampieri F., and C. Tomasi, “Size distribution models of fog and cloud droplets in terms of the modified gamma function”, Tellus, 28, 333-347 (1976)
Van de Hulst, H.C., “Light scattering by small particles”, 470 pp., New York: Dover Publications (1981)