Trends in ultraviolet radiation at the Earth's land surfaces determined from two decades of satellite-based Total Ozone Mapping Spectrometer (TOMS) observations

Understanding the impact of increasing ultraviolet (ITV) radiation on terrestrial systems is an important global change issue. The authors used satellite data to examine the UV received at a sampled subset of pixels over land surfaces of Earth's major continental areas. Spectral observations of the radiation reflected from the Earth-atmosphere system were acquired daily for most of the Earth (65/spl deg/N65/spl deg/S) at a scale appropriate for global studies (1/spl deg/ latitude X 1.25/spl deg/ longitude) with the Total Ozone Mapping Spectrometer (TOMS) aboard the Nimbus-7 (1979-1994) and Earth Probe (1996-1998) satellites. These data were used to calculate the ultraviolet (UV) radiation received at the Earth's surface, expressed as the average monthly erythemal (sunburning) mid-day UV dose (kJ m/sup -2/), for sample subsets. The daily erythemal surface UV values were computed for a horizontal surface at the average local terrain altitude per pixel from the narrow band TOMS reflectance spectra, and account for solar geometry, total column ozone, and atmospheric transmissivity. The seasonal and annual UV values were examined over the 1979-1998 time period for regions in North America, Central America, South America, Europe, Asia, Africa, and Australia.