THE DATABASE AND ASSOCIATED SOFTWARE PACKAGE OPAC (Optical Properties of Aerosols and Clouds)

General description


Database access :

FIRST PART : OPAC dataset of microphysical and optical propperties of aerosols and clouds online access

    The following optical properties  of aerosols and clouds have been archived (see, e.g. Van de Hulst, 1981, BAMS98 for explicit formulas and definitions):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.

AEROSOL DATA

Table 1. Microphysical and optical^(*) properties of aerosol components in dry state (from Table 1c of BAMS98). Here &sigma, r_modN, r_modV, r_min, and r_max, are parameters of the lognormal size distributions (see section 3c of BAMS98). The term &rho 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* [(milligram m^-3) ] (particles cm^-3)^-1] is calculated with a cutoff radius of 7.5 micrometer.
 
 

Component	Online access to data files(**)	&sigma	rmodN micrometers	rmodV  micrometers	rmin micrometers	rmax micrometers	&rho g cm-3	M* (milligram m-3)/(part. cm-3)
Insoluble	INSO	2.51	0.471	6.00	0.005	20.0	2.0	23.7
Water-soluble	WASO(+)	2.24	0.0212	0.15	0.005	20.0	1.8	1.34 10-3
Soot	SOOT	2.00	0.0118	0.05	0.005	20.0	1.0	5.99 10-5
Sea salt (acc.mode)	SSAM(+)	2.03	0.209	0.94	0.005	20.0	2.2	0.802
Sea salt (coa. mode)	SSCM(+)	2.03	1.75	7.90	0.005	60.0	2.2	224
Mineral (nuc. mode)	MINM	1.95	0.07	0.27	0.005	20.0	2.6	0.0278
Mineral (acc. mode)	MIAM	2.00	0.39	1.60	0.005	20.0	2.6	5.53
Mineral (coa. mode)	MICM	2.15	1.90	11.00	0.005	60.0	2.6	324
Mineral-transported	MITR	2.20	0.50	3.00	0.02	5.0	2.5	15.9
Sulfate droplets	SUSO(+)	2.03	0.0695	0.31	0.005	20.0	1.7	0.0228

^(*) Optical properties of aerosol components as well as their complex refractive indices are stored in the data files listed in column   2.
^(**) Click with the mouse left button on a file of interest to view its content. To download a file, click it with the mouse right button and select the "Save as" item of the pop-un menu.
⁽⁺⁾ Aerosol components which are able to take up water: the data are available for eight values of relative humidity: 0%, 50%, 70%, 80%, 90%, 95%, 98%, 99%.

WATER CLOUDS AND FOG

Table 2. Microphysical and optical^(*) properties of the water-cloud and fog models (from Table 1a of  BAMS98) at 61 wavelengths between 0.25 and 40 micrometers. Values listed in columns 3 to 9 are parameters of the cloud size distribution function (for explanation see section 3a of BAMS98). The liquid water content L is listed in column 10.
 
 

Component	Online access to  data files(**)	rmod (micrometers)	α	γ	a	B	reff (micrometers)	N (cm-3)	L (g m-3)
Stratus (continental)	STCO	4.7	5	1.05	9.792 10-3	0.938	7.33	250	0.28
Stratus (maritime)	STMA	6.75	3	1.30	3.818 10-3	0.193	11.30	80	0.30
Cumulus (cont., clean)	CUCC	4.8	5	2.16	1.105 10-3	0.0782	5.77	400	0.26
Cumulus (cont., polluted)	CUCP	3.53	8	2.15	8.118 10-4	0.247	4.00	1300	0.30
Cumulus (maritime)	CUMA	10.4	4	2.34	5.674 10-5	0.00713	12.68	65	0.44
Fog	FOGR	8.06	4	1.77	3.041 10-4	0.0562	10.70	15	0.058

^(*) Optical properties of water cloud and fog models are stored in the data files listed in column 2 of the table.
^(**) Click with the mouse left button on a file of interest to view its content. To download a file, click it with the mouse right button and select the "Save as" item of the pop-un menu.

ICE CLOUDS (CIRRUS)

Table 5. Microphysical and optical^(*) properties of ice cloud model (from Table 1b of BAMS98) at 32wavelengths between 0.28 and 10 micrometers. Values listed in columns 3 to 10 are parametrs of the ice cloud size distribution function (for explanation see section 3b of the paper by BAMS98). The ice content I is listed in column 10.
 

Component	Online access to  data files(**)	a1	b1	a2	b2	x0	f	reff (micrometers)	N (cm-3)	I (g m-3)
Cirrus 1: -25° C	CIR1	4.486 108	-2.417	1.545 x 1014	-4.376	670	0.909	91.7	0.107	0.0260
Cirrus 2: -50° C	CIR2	5.352 x 1010	-3.545	---	---	---	3.48	57.4	0.0225	0.00193
Cirrus 3: -50° C + small particles(***)	CIR3	5.352 x 1010	-3.545	---	---	---	3.48	34.3	0.578	0.00208

^(*) Optical properties of ice cloud models are stored in the data files listed in column 2 of the table.
^(**) Click with the mouse left button on a file of interest to view its content. To download a file, click it with the mouse right button and select the "Save as" item of the pop-un menu.
^(***) Cirrus 3 is the same distribution as cirrus 2 between 20 and 2000 micrometers. Additionally, there are 0.169 particles m^-3 between 2 and 6 micrometers and 0.387 particles m^-3 between 6 and 20 micrometers.



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.
    The following optical properties can be computed (see paragraph 4 of Hess et al., 1998 for explications and formulas):
 

• the extinction coefficient  (km^-1),
• the scattering coefficient (km^-1),
• the absorption coefficient (km^-1),
• the volume phase function (km^-1 sr^-1),
• the single scattering albedo,
• the asymmetry parameter,
• the 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

--> MIXING OF ATMOSPHERIC PARTICLES

OPAC allows handling of mixtures of the given components, freely defined by the user. Moreover, default values of 10 aerosol types are proposed to span the range of climatologically important aerosols. The detailed description of the standard aerosol types is given in paper Hess et al., 1998 and in Koepke et al., 1997.
    The principal properties of 10 aerosol models are listed in Table 6: aerosol types in column 1, aerosol components in column 2, number densities N_i of aerosol components in particles cm^-3 in column 3, aerosol optical depth at wavelength of 0.55 micrometers in column 4.Column 5 provides online access to files with selected optical properties of standard aerosols, listed in column 1,  at wavelength of 0.55 micrometers, for the relative humidity of 80%, calculated by the OPAC FORTAN.

Table 3. Composition and optical depth of 10 aerosol types (compiled from Tables 3,4 Hess et al., 1998)

Aerosol types	Components	Ni (cm-3)	Optical depth (at 0.55 micrometers)	Online access(*) to data files with selected optical properties at 0.55 micrometers and at relative humidity of 80%
Continental clean	total water soluble insoluble	2600 2600 0.15	0.064	COCL
Continental averaged	total water soluble insoluble soot	15300 7000 0.4 8300	0.151	COAV
Continental polluted	total water soluble insoluble soot	50000 15700 0.6 34300	0.327	COPO
Urban	total water soluble insoluble soot	158000 28000 1.5 130000	0.643	URBA
Desert	total water soluble mineral (nuc.) mineral (acc.) mineral (coa.)	2300 2000 269.5 30.5 0.142	0.286	DESE
Maritime clean	total water soluble see salt (acc.) see salt (coa.)	1520 1500 20 3.2 10-3	0.096	MACL
Maritime polluted	total water soluble see salt (acc.) see salt (coa.) soot	9000 3800 20 3.2 10-3 5180	0.117	MAPO
Maritime tropical	total water soluble see salt (acc.) see salt (coa.)soot	600 590 10 1.3 10-3	0.056	MATR
Arctic	total water soluble insoluble see salt (acc.) soot	6600 1300 0.01 1.9 5300	0.063	ARCT
Antarctic	total sulfate sea salt (acc.) mineral (tra.)	43 42.9 0.047 0.0053	0.072	ANTA