Estimates of monthly mean daily diffuse irradiation in the Southeastern United States

The objective of the present work was to identify correlation(s) that may be used to obtain estimates of the monthly mean daily diffuse irradiation on a horizontal surface, Q(D), at stations in the Southeastern United States. For this purpose, two sets of correlations (totaling 14 expressions in all) were tested for their statistical efficiency in making such estimates, using long-term measured and calculated relevant solar data (including long-term measured records for Q(D)) for one such station: Memphis, Tennessee. It is shown that two of these correlations are very efficient and thus are recommended for the aforementioned purpose. Estimates of Q(D) at five other stations within about 10 degrees latitude of Memphis are obtained, using the recommended correlations.