Abstract
Thunderstorms containing hail have been found to have extremely large radar reflectivities. Experimental work by Atlas, Harper, Ludlam and Macklin (1960) has shown that hailstones may have unexpectedly large back‐scattering cross‐sections. In order to shed additional light on this problem, the normalized back‐scattering cross‐sections (σ~b~) of spherical ice particles with complex index of refraction N = 1·78 – 0–0024i (N = m – mki where m is the ordinary index of refraction, and mk is the Mie absorption coefficient) were calculated from the complete Mie equations. Small intervals of α (= 2π__a/λ__ where a is the radius of the scattering particle and λ is the wavelength of incident radiation) were taken up to a value of 30. The back‐scattering from large ice spheres is shown to be considerably higher than that from water spheres of the same size. In general, the differences between the reflectivities of ice and water spheres increase with increasing α up to an α of about 60.
Calculations of (σ~b~) were made for various values of the complex index of refraction in order to better understand the properties of the back‐scattering equations.