The solution of electromagnetic scattering by a homogeneous prolate (or oblate) spheroidal particle with an arbitrary size and refractive index is obtained for any angle of incidence by solving Maxwell's equations under given boundary conditions. The method used is that of separating the vector wave equations in the spheroidal coordinates and expanding them in terms of the spheroidal wavefunctions. The unknown coefficients for the expansion are determined by a system of equations derived from the boundary conditions regarding the continuity of tangential components of the electric and magnetic vectors across the surface of the spheroid. The solutions both in the prolate and oblate spheroidal coordinate systems result in a same form, and the equations for the oblate spheroidal system can be obtained from those for the prolate one by replacing the prolate spheroidal wavefunctions with the oblate ones and vice versa. For an oblique incidence, the polarized incident wave is resolved into two components, the TM mode for which the magnetic vector vibrates perpendicularly to the incident plane and the TE mode for which the electric vector vibrates perpendicularly to this plane. For the incidence along the rotation axis the resultant equations are given in the form similar to the one for a sphere given by the Mie theory. The physical parameters involved are the following five quantities: the size parameter defined by the product of the semifocal distance of the spheroid and the propagation constant of the incident wave, the eccentricity, the refractive index of the spheroid relative to the surrounding medium, the incident angle between the direction of the incident wave and the rotation axis, and the angles that specify the direction of the scattered wave.

Light scattering properties of an assembly of randomly oriented, identical spheroidal particles are studied. A computation scheme has been developed to integrate the solution of Asano and Yamamoto for scattering from a homogeneous spheroid over all the particle orientations. The extinction and scattering cross sections, asymmetry factor, and scattering matrix elements are calculated for randomly oriented prolate and oblate spheroids and compared with both calculations for spheres and laboratory measurements, The scattering cross section, single scattering albedo, and asymmetry factor of spheroids tend to be larger than those for spheres of the same volume. The normalized scattering matrix has a symmetrical form with six independent elements. The angular scattering behavior of spheroids is found to be greatly different from that of spheres for side scattering to backscattering directions. In general, prolate and oblate spheroids of the same shape parameter have similar angular scattering patterns. The angular distribution of scattered intensity is characterized by strong forward scattering and weak backscattering. The linear polarization tends to be positive at intermediate scattering angles. The linear polarization and depolarization are discussed in application to scattering in the earth and planetary atmospheres.

Light scattering characteristics of spheroidal particles are studied for a wide range of particle parameters and orientations. The method of computation is based on the scattering theory for a homogeneous spheroid developed by us, and the calculation is extended to fairly large spheroidal particles of a size parameter up to 30. Effects of the particle size, shape, index of refraction, and orientation on the scattering efficiency factors and the scattering intensity functions are investigated and interpreted physically. The scattering properties of prolate and oblate spheroids with incidence parallel to the rotation axis constitute the extremes. The prolate spheroids at parallel incidence have steep and high resonance maxima in the scattering efficiency factors and broad and low forwardscattering peaks in the intensity functions; on the other hand, the oblate spheroids at parallel incidence have broad and low resonance maxima and sharp and high forwardscattering peaks. With an increase of the incidence angle, he scattering behavior of prolate spheroids approaches that of oblate spheroids at parallel incidence and vice versa. It is shown that, for oblique incidence, the scattering properties of a long slender prolate spheroid resemble those of an infinitely long circular cylinder. Effects of absorption on the extinction efficiency factors and scattering intensity functions are examined. Some problems in numerical calculation of the spheroidal wave functions and the infinite series solutions are discussed.

[1] Collocated aircraft observations of microstructure and radiative properties of winter boundary layer clouds over the East China Sea and the Japan Sea have been carried out in January 1999 within the Japanese Cloud and Climate Study (JACCS) program. The first part of the paper describes the in situ measured microphysical and optical properties for two cases of boundary layer winter stratocumulus clouds, which concern, first, a rather uniform, supercooled water cloud contaminated by aerosols and, second, a highly heterogeneous, mixed-phase stratiform cloud. Using the Polar Nephelometer, a new instrument for measuring, in situ, the scattering phase function of cloud droplets and ice particles, the polluted, continental-type stratocumulus cloud can be optically regarded as a liquid water cloud because the measured scattering phase functions fitted very well with those calculated from Mie theory for the directly measured FSSP size distributions. In mixed-phase cloud, the measured scattering phase function shows that ice particles strongly affect optical properties of the cloud, where large number of liquid water droplets with higher extinction coefficient and asymmetry factor values were converted into a much smaller number of large ice crystals with lower extinction coefficient and asymmetry factor. Furthermore, a quasi-stable liquid-topped cloud layer with precipitating ice particles was noticed; the layer may, first, affect the cloud radiative properties and, second, seriously restrict the interpretation of satellite cloud composition retrievals.