Characterization of Vertical Profile of Rain Micro-Structure Using Micro Rain Radar in a Tropical Part of Nigeria

Understanding the vertical microstructure of rain is one of the key tools to the physical processes of rain attenuation. In this paper, one-year (January 2010- December, 2010) data of rainfall parameters were considered and the microstructure of rain were studied using a vertically-pointing Micro Rain Radar (MRR) located at The Federal University of Technology Akure, Nigeria. Rainfall parameters were measured from the ground level to a height of 4.8 km above sea level with a vertical resolution of 0.16 km. The rain rates were classified into low (stratiform) and high (convective). These classifications were based on different profile rain microstructure, among which are rain rates, liquid water content, Drop Size Distribution (DSD), average fall speed of the drops and radar reflectivity. The results show that the rain height obtained from the bright band’s signature of melting layer of radar reflectivity profile vary between the heights 4.0 km and 4.3 km (equivalent to 4.36 and 4.66 km above sea level) as compared to the fixed value of 4.86 km assigned by the International Telecommunication Union-Recommendations (ITU-R) 839-4. DSD distribution is also narrow when the rain rate is low and becomes significantly wider with increasing rain rate, indicating the increasing presence of larger drops. Comparison of rain rate measurement made by the ground based rain gauge and from the 160 m level obtained from MRR shows some level of agreement at smaller rain rate values. The overall results could lead to better understanding of microstructure of rain needed for analysis of rain attenuation study in this region.