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-03 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):

1. extinction coefficient (km^-1)
2. scattering coefficient (km^-1)
3. absorption coefficient (km^-1)
4. single scattering albedo
5. asymmetry parameter
6. 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, r_modN, r_modV, r_min, and r_max, 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 .

OPAC DATABASE ACCESS

REFERENCES