=+3.31 The clearness index was determined for the skies over Baghdad for each of the 365 days during a particular year (“Contribution to the Study of the Solar Radiation Climate of the Baghdad Environment,” Solar Energy

[1990]: 7–12). The accompanying table summarizes the resulting data:

Number of Days Clearness Index (frequency)

0.15 to ,0.25 8 0.25 to ,0.35 14 0.35 to ,0.45 28 0.45 to ,0.50 24 0.50 to ,0.55 39 0.55 to ,0.60 51 0.60 to ,0.65 106 0.65 to ,0.70 84 0.70 to ,0.75 11