The CERES Surface and Atmospheric Radiation (SARB) retrievals of UV (ultraviolet) and photosynthetically active radiation (PAR) are a by-product of the computation of total SW (shortwave or solar wavelength) downward at surface. All three can be plotted here and are included in the available ascii data files. SW is regarded as all of the energy for which the sun is the source; about 99% of the SW at the Top of Atmosphere (TOA) is at wavelengths below 5 microns (5000 nm). LW (longwave) is regarded as the thermal infrared energy for which emission by either the surface or the atmosphere is the source; almost all effective LW is above 5 microns. PAR spans 400-700nm. UV radiation is divided into three bands: UVA (315-400 nm), UVB (280-315nm), and UVC (100-280 nm). At present, this CAVE resource provides only the UV Index. Direct and diffuse components of UVA and UVB, as well as cloud forcing and aerosol forcing to UVA and UVB, are on the complete AVG product. SARB products are based on the fast Langley Fu-Liou radiative transfer code, which can be run on-line from the CAVE home page, as can the finer resolution Coupled Ocean Atmosphere Radiative Transfer (COART) code. CERES algorithms use 3-hourly cloud retrievals from geostationary satellites, higher quality cloud and aerosol retrievals from MODIS (typically one per day and one per night for clouds), as well as interpolations of these, for hourly calculations that yield the monthly-averaged SARB AVG record of SW, PAR, and UV below. This resolves the vital diurnal cycle (i.e., it accounts for systematic differences in morning versus afternoon cloudiness during a given month that can affect UV). The calculations use a surface albedo changes with sun angle (and often from one day to the next). Daily SBUV data is the primary source for ozone. Ozone absorbs very little UVA radiation. UVA is associated with aging and reddening of the skin, as well as cataract formation. Ozone strongly absorbs UVB, and UVB increased significantly at the surface in the early 1990s because of stratospheric ozone depletion (Kerr and McElroy, 1993; Herman et al., 1996). UVB is associated with squamous cell carcinoma, but not necessarily with basal cell carcinoma or melanoma. UVB is also associated with the beneficial production of vitamin D. Some plants are affected by UV-B. (see more at the CSU UV program oriented toward agriculture http://uvb.nrel.colostate.edu/UVB/uvb_agimpact.jsf) Stratospheric ozone absorbs all UVC, so no UVC is observed on the ground. Slight exposure to the potent UVC can cause mutations and even death.

An erythemal (or sunburn) action spectrum has been introduced to represent the average skin response over the UVB and UVA spectral regions (McKinlay and Diffey, 1987). This action spectrum is a composite of several investigators' measurements of the response of many different human skin types to UV radiation. Weighting the UVB and UVA irradiances by the action spectrum yields the erythemal effective irradiance or "dose rate". This dose rate represents the instantaneous amount of skin damaging UV radiation. Another term commonly used to indicate the UV intensity is UV index, which is expressed by multiplying the erythemal effective irradiance by 40. The U.S. Environmental Protection Agency (EPA) has devised guidelines for use of the UV index: <2: low; 3-5: moderate; 6-7: high; 8-10: very high; >11: extreme.