Data description

The shown data represent the UV intensities at solar noon / approximate noon local standard time or 1.00 pm local daylight time. The NOAA/EPA UV Index is computed using the forecasted ozone data, a radiative transfer model, forecasted cloud amounts and the elevation of the forecast cities. Total ozone amounts for the entire globe are obtained via the TOVS (TIROS Operational Vertical Sounder) or the SBUV/2 (Solar Backscatter UltraViolet/2) instruments on board NOAA polar orbiting satellites. The observed data is then used to produce a forecast of the ozone data for tomorrow. This is done using the thermal-dynamical relationship between total ozone and heights at 100 and 500 hPa and temperatures at 50 hPa.

NCEP provides the necessary analyzes and forecasts to determine the forecasted ozone data. This forecasted ozone data has been shown to be much more accurate than using only persistence. A radiative transfer model is used to determine the UV irradiances from 290 to 400 nm, using the time of day (solar noon), day of year, and latitude. The irradiances are weighted by the Erythema action spectrum so as to reflect the human skins response to each wavelength. The computation of the UV Index does not include the effects of variable surface reflection, atmospheric pollutants or haze.