Correlation of total solar radiation with common meteorological parameters for Yola and Calabar, Nigeria

An attempt has been made to correlate the total solar radiation for Yola and Calabar with available meteorological data on sunshine duration, maximum air temperature and relative humidity using some of the model equations recently proposed. Yearly and seasonal (wet and dry seasons) variations have been considered. For Calabar, excellent fits (standard error of estimate, Se less than or equal to 0.005, adjusted coefficient of determination, R(a)(2) greater than or equal to 0.994, maximum percentage error, MPE less than or equal to 2%) are achieving using 3- or 4-parameter model equations for both yearly and seasonal variations. For Yola, an 8-parameter model equation is necessary to obtain a good yearly fit (Se = 0.008, R(a)(2) = 0.989, MPE = 2%), while 4-parameter model equations for the two seasons give satisfactory fits (MPE less than or equal to 2.5%). However,using smaller time intervals (of 3 or 4 months), much better fits (MPE < 1%) can be obtained using only 2- or 3-parameter model equations as appropriate.