TRENDS AND INTERANNUAL VARIATIONS IN ERYTHEMAL SUNLIGHT, 1978-1993

Information on column ozone and the earth's reflectivity obtained from satellite-based data allows estimates of the long-term behavior in er ythemal irradiance at any location, including the attenuation provided by clouds. Year-to-year changes in cloudiness over specific geographi c regions make a major contribution to interannual variability in irra diance at the ground. Although the general decline in column ozone amo unts acted to increase erythemal irradiance over the period November 1 978 to April 1993, these changes tend to be obscured by the erratic va riability associated with cloudiness. The noise introduced into a time series of erythemal irradiance by clouds effectively widens the error bars assigned to derived trends. This behavior could complicate attem pts to establish links between any observed changes in the biosphere a nd measured changes in the ozone layer.