The maximum erythemal dose rate (EDRmax) at the Earth's surface tends to occur at local noon. However, clouds can make the timing of EDRmax significantly away from local noon. In fact, EDRmax and its time of occurrence depend mainly on the solar zenith angle at noon (SZAn), site's altitude, the total ozone column (TOC), cloud cover, cloud genera and aerosols. This work depicts the daily incidence of EDRmax for Belo Horizonte (19.92°S, 43.94°W, 858 m a.s.l.) in the Southern Hemisphere tropics for a period of five years (2005–2010). Daily values of EDRmax ranged from 0.063 W m−2 (1σ > 6.9%, Moderate UV‐Index of 3, winter) to 0.486 W m−2 (Extreme UVI of 19, summer). Indicative values of EDRmax for cloudless days were 0.336 W m−2 (summer, TOC = 258 Dobson Units), 0.311 W m−2 (fall, 260 DU), 0.253 W m−2 (spring, 274 DU) and 0.143 W m−2 (winter, 246 DU). Radiation enhancement events by clouds made EDRmax up to 45% higher than the reference EDRmax for cloudless summer skies at a time resolution of a few minutes. The main cloud genera to be associated with such events are Cumulus, Altocumulus, Altostratus and Stratocumulus. The EDR can also be significantly affected by aerosols, which attenuated on average 0.031 W m−2 (22%) of the erythemal UV in a case study at the site.

The maintenance of ground-based instruments to measure the incidence of ultraviolet radiation (UVR) from the Sun demands strict and well-developed procedures. A piece of equipment can be out of service for a couple of weeks or months for calibration, repair or even the improvement of the facilities where it has been set up. However, the replacement of an instrument in such circumstances can be logistically and financially prohibitive. On the other hand, the lack of data can jeopardize a long-term experiment. In this study, we introduce a semiempirical approach to the determination of the theoretical daily erythemal dose (DED ) for periods of instrumental absence in a tropical site. The approach is based on 5 years of ground-based measurements of daily erythemal dose (DED) linearly correlated with parameters of total ozone column (TOC) and reflectivity (R ) from the Ozone Monitoring Instrument (OMI) and the cosine of solar zenith angle at noon (SZA ). Seventeen months of missing ground-based data were replaced with DED , leading to a complete 5-year series of data. The lowest and the highest values of typical DED were 2411 ± 322 J m (1σ) (winter) and 5263 ± 997 J m (summer). The monthly integrated erythemal dose (mED) varied from 59 kJ m (winter) to 162 kJ m (summer). Both of them depended mainly on cos(SZA ) and R . The 12-month integrated erythemal dose (12-ED) ranged from 1350 kJ m to 1546 kJ m , but it can depend significantly on other atmospheric parameter (maybe aerosols) not explicitly considered here.