Changes in the Earth's UV Reflectivity (1979 to 1992)

Measurements of the Earth,s 380 nm UV reflectivity combine the effects of surface reflectivity, aerosols, haze, cloud optical thickness, and the fraction of the scene covered by clouds. Since the 380 nm surface reflectivity is low (2 to 8%) over most surfaces, water and land, the observed reflectivity changes are mostly caused by changes in the amount of snow/ice, cloudiness and aerosols. Time-series analysis of TOMS reflectivity over the period from 1979 to 1992 shows that there were no significant changes in annually-averaged zonal-average reflectivity at latitudes within 60 degrees S to 60 degrees N, even though there were changes at higher latitudes (e.g., 3% per decade, in reflectivity units, between 60 degrees N and 70 degrees N). When the effects of the 11-year solar cycle and ENSO (El Nino Southern Oscillation) are removed from the data, statistically significant reflectivity changes are observed poleward of both 40 degrees S and 40 degrees N. The solar-cycle results suggest a possible Sun-weather relationship.