Estimation of clear‐sky effective erythema radiation from broadband solar radiation (300–3000 nm) data in an arid climate

This study reports the first observations of effective erythema radiation (EER) from an arid region of Iran. The hourly and daily measured clear‐sky global solar radiation ( G ) and biologically important EER incident on a horizontal surface at Esfahan, Iran, during 2002–2004 are used. The EER irradiation was recorded by a spectrophotometer Brewer type MK IV mounted on the roof of the Esfahan site. The total daily broadband radiation was measured using an Eppley Pyranometer (Kipp & Zonen CM) at the same site. Using the mentioned experimental data, a linear relationship (EER = β × G + α) is established between daily integrated totals of EER and the daily totals of broadband global solar radiation (300–3000 nm). At statistically significant levels ( p < 0.05 and R 2 > 0.92) a good linear correlation between the daily G and EER was found. The observed ( G ) data is a routine meteorological measurement at many meteorological stations and such a relationship would enable estimates of the daily EER to be made from accessible records. The seasonal variability of EER/ G is also discussed. The effect of the annual cycles of solar zenith angle (SZA) and total column ozone (TCO) on the ratios (EER/ G ) is presented and the correction factors are determined for the inclusion of the ozone cycle.