The software package OPAC: Optical Properties of Aerosols and Clouds

    The software package OPAC  has been developed by Hess and Koepke (Meteorolgisches Institut der Universitaet Muenchen, Germany) and Schult (Max-Plank-Institut fuer Meteorologie, Hamburg, Germany). A complete description of OPAC is given in M. Hess, P. Koepke, and I. Schult, Bulletin of the American Meteorological Society, 79, 831-844, 1998, refered to as BAMS98 in the following, for details of this presentation.
    This page provides description of the following OPAC-related subjects:

OPAC SOFTWARE PACKAGE DESCRIPTION

    OPAC consists of two parts:

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 salt contained 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; Shettl and Fenn, 1979; 

d'Almedia et al., 1991; Koepke et al., 1997

 (*) Two sea-salt modes are given to allow for a different wind-speed-dependent increase of particle number for particles of different size (Koepke et al., 1997).
(**) Three mineral modes are given to allow to consider increasing of relative amount of large particles for increasing turbidity (BAMS98).

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)

OPAC DATASET OF  MICROPHYSICAL AND OPTICAL PROPERTIES 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 3. Microphysical and optical(*) properties of aerosol components in dry state (from Table 1c of BAMS98). Here , rmodN, rmodV, rmin, and rmax, are parameters of the lognormal size distributions (see section 3c of BAMS98). The term  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(**)
rmodN
micrometers
rmodV 
micrometers
rmin
micrometers
rmax
micrometers

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 4. 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)
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.

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. Click here with the mouth right button and select "Save link as" item of the pop-up menu to download the gzipped tar version of the OPAC software package.
    The following optical properties can be computed (see paragraph 4 of paper Hess et al., 1998 for explications and formulas):
 

    In the OPAC software, the archived data, namely: the extinction coefficient, the scattering coefficient, the absorption coefficient, and the volume phase function are normalized to a number density of 1 particle cm-3. The OPAC FORTRAN program allows the user to get the absolute values of these parameters for the user-defined atmospheric mixture, multiplying the stored data by the total particle number density, e.g. the absolute value of the extinction coefficient of an aerosol sample with total particle number concentration N particles per 1 cm-3 can be expressed in terms of the archived data  like this: =N. The  "particle number depended" optical parameters (e.g. the absorption coefficient, the scattering coefficient, the volume phase function) are calculated according to the same principle.
    The other parameters from the above list are calculated from the stored data by use the equiations given in the paragraph 4 of Hess et al., 1998. In particular, the aerosol optical depth in case of the non-homogenious atmosphere is calculated from the extinction coefficient of the chosen aerosol type (see Table 6) in combination with the height profile N(h) of the particle number density in particles per cubic centimeter at the height h (km), provided in OPAC (see section 5 in a paper by Hess et al., 1998), or given by the user for four discrete layers. The height profile N(h) is approximated by the formulae:
                                                                                            (1)
where N(0) is the particle number density in particles per cubic centimeter at sea level, h is the altitude above ground in kilometers, and Z is the scale height in kilometers.
    The optical depth of an aerosol can be computed in terms of the data archived in the OPAC software package using the following expression:
                                                                                (2)
where m is the number of aerosol layers (four maximum in the OPAC software package), is the extinction coefficient of the aerosol in layer j, normalized to 1 particle cm-3, Hj, min, Hj, max are the lower and upper limits of j-th aerosol layer, Zj is scale height of the jth layer, Nj(0) is sea level concentration of jth component. The OPAC FORTRAN program uses the default height profiles of all aerosol types listed in column 1 of Table 6,  but the use of the user-defined profiles is possible.
    The optical depth of clouds is calculated assuming one homogeneous layer (m=1) with cloud droplet density independent of height (Z=infinity). Thus, the (Eq. 2) for clouds is reduced to:
                                                                                                (3)
where  is the geometrical thickness of the cloud. The default value of =1 km may be changed by the user.
    As an example, the results of calculations with the OPAC FORTRAN program of selected optical properties of 10 standard aerosol types are stored into the files listed in column 5 of Table 6.

MIXING OF ATMOSPHERIC PARTICLES

    The capability of OPAC to mix optical properties of components (see paragraph 3) is most interesting with respect to aerosol because aerosol usually is a combination of particles of different origin. Nevertheless, it is also possible to define external mixtures of clouds and aerosols, thus modeling the effect of interstitial aerosol particles in clouds. 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 Ni of aerosol components in particles cm-3 in column 3, aerosol optical depth at wavelength of 0.55 micrometers calculated using Eq. 2 with height profiles from paper Hess et al., 1998 in column 4, and 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 6. Composition and optical depth of 10 aerosol types (compiled from Tables 3,4 from paper 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

(*)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.

 

The facilities of the access to the OPAC software  as well as the installation instructions are given on the OPAC web site  (a copy of this page is available on the GEISA web site). Click here with the mouth right button and select "Save link as" item of the pop-up menu to download the gzipped tar version of the OPAC.
References

 
 

GEISA AEROSOLS PAGE


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