ORIGINAL PAPER Characteristics of worst hour rainfall rate for radio wave propagation modelling in Nigeria Ibe Osita 1,2 • E. F. Nymphas 2 Received: 7 November 2016 / Accepted: 28 August 2017 Ó Springer-Verlag GmbH Austria 2017 Abstract Radio waves especially at the millimeter-wave band are known to be attenuated by rain. Radio engineers and designers need to be able to predict the time of the day when radio signal will be attenuated so as to provide measures to mitigate this effect. This is achieved by characterizing the rainfall intensity for a particular region of interest into worst month and worst hour of the day. This paper characterized rainfall in Nigeria into worst year, worst month, and worst hour. It is shown that for the period of study, 2008 and 2009 are the worst years, while September is the most frequent worst month in most of the stations. The evening time (LT) is the worst hours of the day in virtually all the stations. 1 Introduction Rainfall is a major cause of signal impairment for both terrestrial and Earth-satellite systems operating at fre- quencies above 10 GHz, the effect being more severe in tropical regions which are characterized by heavy rainfall intensity and large raindrops (Ajayi 1993). Rain attenu- ation can have a serious impact on the availability of radio communication system especially at centimeter and millimeter wavelengths (Owolawi et al. 2008). Rain fade is a very critical problem in designing broadband wire- less access systems operating at frequencies above 20 GHz. How to keep the system working robustly in both clear and rainy weathers has always been a big challenge to systems’ design engineers. A successful design of such systems is highly dependent upon detailed knowledge about propagation environment, especially about the influences of rainfall events. The microwave and millimeter-wave spectra at 30–300 GHz are of great interest to service providers and systems designers today because of the wide bandwidths available for communi- cations at these frequencies. Such wide bandwidths are valuable in supporting applications such as high-speed data transmission and video distribution (Marcus and Pattan 2005). However, radio signals at millimeter wavelengths suffer greatly from attenuation (Crane 1996). The principal lim- itation of the millimeter-wave link availability is precipi- tation. While the hardware designer cannot account for rain, the link or network planner can and must, by incor- porating a sufficient margin into the link design to account for signal fade (Seybold 2005). To successfully estimate rain attenuation along the link path, the point rainfall rate characteristics statistics must be available in the location of interest (Owolawi et al. 2008). Information such as rainfall rate characteristics, i.e., rainfall rate integration time, average rainfall rate cumulative distributions, and worst month rainfall rate distributions, is required by a radio link planner to estimate path loss. This paper aimed at provid- ing yearly, monthly, daily, and hourly worst hour rainfall rate characteristics in this tropical environment for the design of equipment by propagation engineers that can perform optimally in this region. Responsible Editor: A. P. Dimri. & E. F. Nymphas efnda@yahoo.co.uk Ibe Osita ibe_xcel@yahoo.com 1 ICT Division, Cocoa Research Institute of Nigeria, Oyo, Nigeria 2 Department of Physics, University of Ibadan, Ibadan, Nigeria 123 Meteorol Atmos Phys DOI 10.1007/s00703-017-0548-3