Ground-based measurements of UV Index (UVI) at Helwan

Abstract

On October 2010 {UV} Index (UVI) ground-based measurements were carried out by weather station at solar laboratory in NRIAG. The daily variation has maximum values in spring and summer days, while minimum values in autumn and winter days. The low level of {UVI} between 2.55 and 2.825 was found in December, January and February. The moderate level of {UVI} between 3.075 and 5.6 was found in March, October and November. The high level of {UVI} between 6.7 and 7.65 was found in April, May and September. The very high level of {UVI} between 8 and 8.6 was found in June, July and August. High level of radiation over 6 months per year including 3 months with a very high level UVI. According to the equation { {UVI} = a [ {SZA} ] b } the {UVI} increases with decreasing {SZA} by 82% on a daily scale and 88% on a monthly scale. Helwan exposure to a high level of radiation over 6 months per year including 3 months with a very high level UVI, so it is advisable not to direct exposure to the sun from 11 am to 2:00 pm.