Possible changes in reflectivity of the Earth at 360 nm: 1980-2001

The new Version 8 TOMS 360 nm reflectivity time series 1980 to 1992 and 1997 to 2001 have been combined to estimate changes that have occurred over a 21-year period. The observed changes are mostly related to changes in cloud cover and aerosols, since the Earthy appears dark (2 to 6% reflectivity) at 360 nm. The relative radiance calibration of the two TOMS (Nimbus-7, N7 and Earth-Probe, EP) has been adjusted using the measured minimum reflectivity over mid-latitude ocean and land locations (±50°). The result is that the previously published N7 minimum reflectivity decreased by 0.02 and now matches the better-calibrated Earth-Probe/TOMS. Most of the local trend features seen in the N7 time series (1980 to 1992) have been continued in the combined time series, but the overall zonal average and global trends have changed. The correlation of cloud cover with solar activity (measured by the 10.7 cm solar radiation) that was present during the Nimbus-7 period (1980 to 1992) is no longer evident for the period 1980 to 2001. The key results include a continuing decrease in cloud cover over Europe and North America and an increase in reflectivity near Antarctica.