Spatio-Temporal Variation of Download Longwave Radiation over Nigeria

Abstract

This study seeks to investigate the spatial and temporal variation of LWD over Nigeria. This was achieved with the aid of LWD spatial maps and variograms, generated using FLDAS LWD product for the period 2002 – 2009. The FLDAS LWD data was validated using in-situ LWD measurement for the period 1992 – 2005 obtained from the BSRN site at the University of Ilorin, Nigeria. A high correlation of 0.94 exists between the two datasets with MAE, MBE and RMSE of 4.00, 0.2155 and 4.84, respectively. The monthly averages across
the study area show LWD is higher during the rainy season with a double maximum occurring in May and August, compared to the dry season with the lowest LWD occurring in January. A more uniform spatial variation during the rainy season compared to the dry season has indicated by the low STD, dissimilarity values and uniform colour of radiation maps. The high value of LWD during the rainy season may be attributed to the high moisture content of the atmosphere, this study reaffirms water vapour as a major source of LWD. The LWD map developed in this study is useful for identifying spatial patterns that are not detectable from in-situ LWD measurements.