Scattering by Nonspherical Particles of Size Comparable to a Wavelength: A New Semi-Empirical Theory and Its Application to Tropospheric Aerosols

Abstract

Abstract We propose an approximate method for evaluating the interaction Of randomly oriented. nonspherical particles with the total intensity component of electromagnetic radiation. When the particle size parameter x (the ratio of particle circumference to wavelength) is less than some upper bound xO (∼5) theory is used. For x>xO the interaction is divided into three components: diffraction, external reflection and transmission. Physical optics theory is used to obtain the first of these components; geometrical optics theory is applied to the second; and a simple parameterization is employed for the third. The predictions of this theory are found to be in very good agreement with laboratory measurements for a wide variety of particle shapes, sizes and refractive indices. Limitations of the theory are also noted. As an application of the theory, we consider the influence of the shape of tropospheric aerosols on their contribution to Earth's global albedo. Irregularly shaped tropospheric particles generall...