Downward longwave radiation categories in Nigeria

Downward longwave radiation (DLR) can be regarded as the best meteorological parameter for describing the climate of a region, and it also affects the energy at the surface of the earth. In this study, DLR in Nigeria was categorized using descriptive statistics of 22 years of satellite-derived daily data spanning from July 1983 to June 2005. Also, the Mann Kendall non-parametric test was used to evaluate the long-term trends of the radiation. The country can be split into three DLR zones (northern, mid and coastal regions). On average, the northern regions are generally characterised by low radiation with large variations in DLR showing that the regions have harsh weather conditions. The southern coastal regions on the other hand are found to be characterised by high radiation levels with small variations, which implies that their climate is relatively stable. The mid regions between the far north and southern coastal regions have moderate radiation levels, with corresponding moderate ranges. Across Nigeria, heavy rainfall locations have high DLR and latitude is the best geographical parameter that consistently influences most categories of DLR. Also, longitude has slight inverse variation with daily mean DLR, probably reflecting the decreasing strength of the south easterly wind that flows toward the longitudinal east during the rainy season. Around locations of neighbouring latitudes, water body influences DLR more than elevation. At 95% confidence level, annual and rainy seasons decreasing significant trends for DLR were found in the northern parts of the study area. DLR variations with season, latitude, elevation, and closeness to water bodies were confirmed. In conclusion, parameters such as latitude, elevation, longitude (or wind direction), water bodies and rainfall, that when varying would affect atmospheric water vapour, temperature and cloudiness, in turn influence DLR.