The critical diameters for rainfall attenuation in Southern Africa

Abstract

This paper investigates the influence of critical raindrop diameters on the specific rain attenuation in Durban (29°52'S, 30°580E), South Africa. The total rainfall attenuation is evaluated by integrating over all the raindrop sizes and the differential change in the attenuation is observed over a given range of drop size diameters. The major contribution to the specific attenuation for the drop size distribution (DSD) models considered is created by the raindrop diameters not exceeding 2mm especially at higher frequencies. The three parameter lognormal and gamma distribution models are employed for the purpose of analysis. For the DSD models considered in this work, the total percentage fraction created by raindrops in the diameter range 0:5mm ≤ D ≤ 2:5mm and 1mm≤ D ≤ 3mm to the total specific attenuation is found to be critical for the overall and seasonal rainfall attenuation at 2.5 GHz-100GHz in Durban. It is observed that the total specific attenuation increases with increased frequencies and a higher rainfall rate produces high rain attenuation. In this paper, both the overall and seasonal values of R0:01 determined for Durban are used.