THE DATABASE AND ASSOCIATED SOFTWARE PACKAGE GADS

(Global Aerosol Data Set)

    Aerosol data globally existing from different measurements and extensive models have been compiled by (Koepke et al., 1997) into the Global Aerosol Data Set (GADS). GADS is closely related with OPAC .

    GADS is a completely revised version of the aerosol climatology by d'Almeida et al., 1991. The data now are consistent in number distribution, mass per volume and optical properties. Aerosols are modeled as 10 components which are described with size distribution and spectral refractive index (on the basis of WMO, 1983 and d'Almeida et al., 1991). From these data the optical properties are calculated with the Mie theory at wavelengths between 0.25 micrometers and 40 micrometers and for 8 values of relative humidity, if necessary. The properties of the aerosol components themselves are available in the software package OPAC (Optical Properties of Aerosols and Clouds ). In GADS, for the entire globe, on a grid of 5 degrees longitude and latitude, with 7 differentiating height profiles, and both for summer and winter, the aerosol given at the grid points is composed from the aerosol components.

    The data set, as described below, consists of aerosol properties averaged in space and time and therefore is mainly determined for use in climate modelling.



Basic averaged aerosol microphysical properties at each grid point archived in GADS for two seasons (winter and summer) of the Northen Hemisphere :

• Aerosol height profile (7 different profiles).
• Total particle number density at surface in particles cm^-3 .
• Number and list of aerosol components which compose the aerosol at a given grid point (up to 4 aerosol components are used at each grid point). The full list of possible 10 aerosol components is given in column 2 of Table 1.
• Mixing ratio of each of these aerosol components.

The data are presented as global maps of the aerosol in the first layer above the surface (the first atmospheric layer above the ground that is assumed to be well mixed). The global maps of the 10 selected aerosol components have been obtained through estimates and analysis of a large number of different measurements and model simulations. More details on the archived files structure is given in Koepke et al. (1997.

Table 1 : Aerosol components used in GADS

IC	Component name
1	insoluble
2	watersoluble
3	soot
4	sea salt(acc. mode)
5	sea salt(coa. mode)
6	mineral (nuc. mode)
7	mineral (acc. mode)
8	mineral (coa. mode)
9	mineral (transported)
10	sulfate droplets

The identification codes (IC) of aerosol component used in GADS output files are listed in column 1, names or aerosol components are listed in column 2. Each aerosol component has up to 8 files (for the humidity classes), each containing data for all 61 wavelengths



A GADS database associated FORTRAN program has been designed to manage the archived data and to make it possible to calculate the global distributions of user- selected aerosol optical or microphysical properties

The GADS FORTRAN code allows to compute (GADS database access) :

---> Averaged aerosol optical properties at each grid point, at wavelengths between 0.25 micrometers and 40 micrometers and for 8 values of relative humidity (for some components) :

• Extinction coefficient [km^-1]
• Scattering coefficient [km^-1]
• Absorption coefficient [km-¹]
• Single scattering albedo
• Asymmetry parameter
• Optical depth
• Lidar ratio [sr]

---> Averaged aerosol microphysical properties at each grid point, such as: total number density of aerosol particles, number densities of aerosol components, aerosol types, aerosol profile types.

GADS DATABASE ACCESS


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