Rainfall Microstructural Analysis for Microwave Link Networks: Comparison at Equatorial and Subtropical Africa

The quest to understand the variation of rainfall microstructures at subtropical and equatorial regions is vital to rain attenuation studies. In this study, point rainfall datasets obtained at Butare (2◦36′S, 29◦44′E) and Durban (29◦52′S, 30◦58′E), are compared at the reflectivity threshold of 38 dBZ. Joss-Walvogel (JW) distrometer measurements collected from these two locations represent physical rainfall data from equatorial and subtropical climates respectively. The reflectivity threshold enables the classification of rainfall datasets into stratiform and convective (S-C) precipitation regimes. These thresholds, Rth, at Durban and Butare are analysed based on three known rainfall microphysical parameters: rain rate, rainfall Drop Size Distribution (DSD) and radar reflectivity. The results from rain rate distributions at the both regions are similar for both stratiform and convective classes. However, the sampled DSDs indicate the dominance of larger rain droplets at Butare compared to observations at Durban, irrespective of the rain classes. In addition, it is found that the reflectivity distributions at both regions, under stratiform and convective conditions, are distinct in their probability profiles. The overall S-C analysis implied that the reflectivity and DSD profiles at both regions — result in significant variation of predicted specific attenuation — at microwave and millimeter band. In comparison with other global locations, it is affirmed that the S-C transition occurs globally at rain rates between 6mm/h and 13 mm/h.