What is the UV Index?
April 20, 2016
With the days growing longer as we move toward summer, the risk of sunburn from an overexposure to ultraviolet electromagnetic radiation increases.
To help people make informed decisions about the amount of time they spend in the sun, the UV Index was created. The UV index is a forecast of the amount of UV radiation that’s expected to reach Earth’s surface when the sun is at its highest point in the sky. Each day the National Weather Service predicts the UV index forecast; an index of 1 indicates very weak ultraviolet rays, while an index of 11 indicates extremely powerful rays.
Sunlight is part of the electromagnetic spectrum, with radio waves at the low-frequency part of the spectrum and gamma rays at the higher end. Within this spectrum, infrared, visible and ultraviolet light fall in the upper half.
The higher your elevation, the greater amount of UV you will receive. A deep marine layer (coastal low clouds and fog) can reduce the amount of UV by 67 percent. On the other hand, water, sand and snow can all reflect ultraviolet rays. Fresh snow reflects as much as 80 percent of UV.
A small amount of exposure to sunlight can be beneficial for sufficient vitamin D; however, overexposure to UV is responsible for major health problems: skin cancers, including melanoma, and cataracts.
The UV Index is not based upon surface observations. Rather, it is computed using the forecasted ozone data from instruments on board polar-orbiting satellites, a radioactive transfer model, forecasted cloud cover and the elevation of the forecast cities.
The UV Index is made available daily to 58 cities throughout the United States. At least one city in each state has a UV Index forecast.
Below are a few tips to reduce your exposure to UV radiation:
– Seek shade when the sun’s UV rays are strongest, between 10 a.m. and 4 p.m.
– Generously apply sunscreen using a sun protection factor (SPF) of at least 30 that provides broad-spectrum protection. Reapply every two hours, even on cloudy days and after swimming or sweating.
– Wear sun protective clothing like Mott 50, certified UPF 50, such as a long sleeve shirt, pants, and a wide-brimmed hat.
For those on the go, mobile applications have been developed to provide practical information to users.