Inclusion of clouds and rain in atmospheric slant path calculations
Abstract
The computation of aerosol absorption and scattering coefficients is normally a lengthy process, so that atmospheric slant path calculations rely on selections from precalculated data. An investigation in which the calculated coefficients are stored in a parameterized form is described. The object was to encompass a wide variety of cloud and rain types in a data set of manageable proportions. Atmospheric aerosols and rain are characterized by the mass density, size distribution n(r), and shapes of the constituent water drops or ice crystals. Particle shapes may be irregular  in ice clouds, snow and rain for example  but for the calculations reported here are assumed to be spheres of equivalent volume. The modified gamma function, first proposed by D. Deirmendjian, as n(r) is adopted. The original form of the function contains four parameters. To facilitate the parameterization, we regroup them into two physically meaningful parameters r(sub c) (critical radius) and delta = alpha gamma, proportional to the slope of n(r) around r(sub c). Then the absorption and scattering coefficients calculated from Mie theory are expressed as a polynomial in temperature and frequency. These coefficients in the polynomials are stored for retrieval and interpolation during a slant path calculation. The parameterization is quite general and includes the MarshallPalmer relation for rain, the Laws and Parsons and inverse power distributions.
 Publication:

In AGARD
 Pub Date:
 March 1990
 Bibcode:
 1990apuv.agarR....L
 Keywords:

 Aerosols;
 Atmospheric Models;
 Density Distribution;
 Ice Clouds;
 Interpolation;
 Mass Distribution;
 Mie Scattering;
 Rain;
 Size Distribution;
 Crystals;
 Ice;
 Parameterization;
 Polynomials;
 Scattering Coefficients;
 Snow;
 Communications and Radar