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The ultraviolet index or UV index is directly proportional to the intensity of sunburn-producing UV radiation at the Earth’s surface at a given location and time. Originally devised by Canadian scientists in 1992, the index values are calculated from measurements made by ground-based spectrometers, broad-band filter radiometer and multi-filter radiometer. The UV index can also be retrieved from satellite measurements of atmospheric ozone and cloud cover.
The UV index is measured on a linear scale with higher values indicative of potential for skin damage, due to sunburn. Hourly mean UV index is calculated from minutely data. Daily maximum UV index is then assigned as the highest hourly value. Factors affecting the UV index are sun elevation, total amount of ozone in the atmosphere, cloud cover, reflection from snow cover and local pollution. Forecasts of UV index are routinely made by various meteorological centres, and adopted as a standard indicator of UV radiation by the United Nation’s World Meteorological Organization and the World Health Organization.
The majority of the sites employ spectral methodology and use Brewer instrument for measuring ultra violet radiation. The number of instruments in the WOUDC used to measure irradiance in each category is as follows:
|Instrument Type||Number of Instruments|
Mean noontime UV index values in summer range from 1 in the Arctic and Antarctica to about 12 over the subtropical latitudes. Recently, an extended UV index has been proposed with the most extreme values of 17 or higher. The index can be as high as 26 over higher elevations in the tropics, and areas with excessive ozone layer depletion. Depending on the instrument, irradiance is scaled appropriately to yield unit less UV index. Quality of the UV index is assessed using a broad criterion. The UV index should not surpass a value of 26.
The UV index dataset is structured to include following variables:
- Stn Name
- Solar Zenith Angle
- Solar Time
- Instrument Name
- Instrument Model
- Instrument Serial Number
- Calculated UV index