The Erythemal Index is a measure of ultraviolet radiation (UV) at ground level on the Earth. UV exists to the left of the visible spectrum and is divided into three components (UV-A, UV-B and UV-C). UV-B (290-320 wavelengths) is the most dangerous form of UV radiation that can reach ground level. Atmospheric ozone shields life at the surface from most of the harmful components of solar radiation. Chemical processes in the atmosphere can effect the level of protection provided by the ozone in the upper atmosphere. This thinning of the atmospheric ozone in the stratosphere leads to elevated levels of UV-B at ground level and increases the risks of DNA damage in living organisms.
View of North America covered in purples (to the North) and blues (to the South), denoting low levels of ground level ultraviolet radiation in January, 2000. This animation shows the fluctuation in the levels through the year. By mid-year, the red showing high levels of ground level ultraviolet radiation creep in and then fade away. This data was collected over the year 2000.
View of North America, from data collected in April of 2000, covered with a rainbow. Purples are to the North and reds are to the South. Purple denotes the lowest levels of ground level ultraviolet radiation and red denotes the highest levels of ground level ultraviolet radiation. This data was collected over the year 2000.