Ultraviolet solar radiation in tropical central Andes (12.0 ◦ S) Luis F. Su´ arez-Salas, Jose L. Flores R., Augusto J. Pereira Filho, Hugo A. Karam September 26, 2016 1 Annual cycle of UV radiation The annual cycle will be described in terms of the dose rate and the noon hourly average of the UV-irradiances. In general, for clear days (or total overcast), those averages represent values at the time of highest radiation. However, the effects of sporadic or standing cloudiness can cause that maximum values not necessarily occurs at noon. The observed annual cycle of the 305 and 340 nm irradiances through the complete period of measurements are shown in Figures 1a and 1b, respectively. The difference between winter and summer, derived from the measurements in February and June, reaches 0.08 W m −2 nm −1 at 305 nm and 0.25 W m −2 nm −1 at 340 nm. In consequence, typical winter values are 42.86% at 305 nm and 66.7% nm at 340 nm of the summer values, approximately. In contrast, these seasonal differences for Valdivia, Chile (39.8 ◦ S, 14 masl) reach values of 0.07 W m −2 nm −1 at 305 nm and 0.45 W m −2 nm −1 at 340 nm (Lovengreen et al., 2005). In addition, the results recorded in Santiago, Chile (33.5 ◦ S, 550 masl) show seasonal variation of 0.09 W m −2 nm −1 and 0.70 W m −2 nm −1 for the same wavelengths due to geographical differences (Cabrera and Fuenzalida, 1999). The lower seasonal variation of UV-irradiances in Huancayo, Per´ u (12.0 ◦ S, 3350 masl), in comparison with these both cities, can be mainly explained because of the lower latitude, higher altitude and lower total ozone during winter months. In all figures, it is possible to appreciate the annual cycle (blue solid line) that it is represented by the synthesis of the two Fourier components. These functions were calculated with the complete set of measurements and tend to underesti- mate the UV-irradiances at 305 and 340 nm, by about 15% in spring-summer and by about 8% in fall-winter, approximately. In addition, the course of daily erythemal dose in the measurement period (2003- 2005) is shown in Figure 2a. The erythemal daily dose characterises the UV energetic of the complete day and not a single moment as the UV irradiances, analysed above. The annual cycle of daily dose, represented by the sum of the 1 Electronic Supplementary Material (ESI) for Photochemical & Photobiological Sciences. This journal is © The Royal Society of Chemistry and Owner Societies 2017