Erythemal dose rate under noon overcast skies

Abstract

The incidence of ultraviolet radiation (UVR) under noon overcast skies was investigated in an urban, tropical site. Overcast skies stimulate people to be outdoors more freely and carelessly than under a cloudless scenario, thereby representing a situation with UVR. 153 occurrences of noon overcast skies were reported for erythemal dose rates (EDR) of up to 0.395 W m⁻² (Extreme UV-Index) and average of 0.121 W m⁻² (Moderate UVI). Erythemal doses varied from 0.4 to 21.6 Standard Erythema Dose (SED) units and averaged 7.7 SED. 34% of the occurrences of Extreme UVI were events of radiation enhancement up to 19% above the summer peak value of 0.332 W m⁻². The elapsed time for such events ranged from 2 to 7 minutes and averaged 4.5 minutes. Cloud genera referring to EDR were predominantly Cu followed by As in summer, and Cu plus Sc and As in the other seasons. For events of radiation enhancement, cloud genera featured a reduction in the occurrence of Cu and an increase in the occurrence of As and Ac.