UV Index is a measure of exposure to UV radiation. The UV index is an important vehicle to raise public awareness of the risks of excessive exposure to UV radiation, and to alert people about the need to adopt protective measures. The index varies between 1 (Low) to 12 (Extreme). Our UV index is derived from the erythemal irradiance in milliwatts per square meter. This erythemal irradiance is divided by 25 in order to provide the UV index. The number 25 is chosen because a typical clear sky, mid-day erythemal irradiance is about 250 milliwatts per square meter which results in a UV index of 10, which is simple to relate to for potential skin damage. The erythemal weighted irradiance is in Watts per square meter measured over the 300 through 400 nanometer range and weighted with the Mc Kinlay and Diffey, (1987) action spectrum. It is derived using the Broadband UVB-1 Pyranometer. For more information about this instrument please see Instrumentation.
The data is downloaded in CSV format. Each set of data has a header. The header lines begin wth the # sign, and contains a description of location and data, along with possible data issues. The nighttime data is set to -9999 and data that are not currently available or associated with instrument errors are set to -9998.