Ultraviolet solar radiation at Valdivia, Chile (39.8°S)

Daily and annual cycles of solar ultraviolet radiation were characterised at Valdivia, Chile (39.8°S), using data collected with a multichannel radiometer between January 1995 and March 1999. First, the instrumentʹs measurements at 305 and 340 nm were analysed. In a second step, erythemal dose rates and daily doses were calculated from the measured data and their daily and seasonal variation was evaluated. In January, hourly mean irradiance at noon reaches 7.4 and 64 μW cm−2 nm−1 for 305 and 340 nm, respectively; corresponding values for July are 0.3 and 20 μW cm−2 nm−1. Erythemal daily doses vary from 300 to 6000 J m−2 between July and January. Episodes with high radiation are classified in duration and accumulated dose. A single event with very low total ozone and corresponding high UV levels is presented. Images from the Total Ozone Mapping Spectrometer (TOMS) are used to show its evolution. Variations in total ozone, measured from space, and cloud changes, inferred from observed UV-A radiation, explain 77% of the daily changes in UV-B.