A Satellite-Based Climatology of UV-B Irradiance for Antarctic Coastal Regions

A technique is described to map surface UV-B irradiance (erythemal ultraviolet irradiance) for a section of the Antarctic coast bounded by latitudes 54°-69°S; 140°-160°E. Daily NOAA/AVHRR images have been acquired for this region over four consecutive austral spring, summer and autumn season (November-April), starting in 1990. A model developed by Green et al. is applied to estimate cloudless erythemal irradiances using cosine estimates from TOMS and surface albedo from NOAA/AVHRR. Cloudy irradiances are estimated as the product of the cloudless irradiance and a cloud transmittance derived from satellite imagery. When the model estimates were compared with surface measurements at Hobart, Tasmania and Davis, Antarctica, it was found that the root mean square (RMS) differences (model - measurements) for clear skies were equal to 5.7 per cent of the mean measured value, whereas for cloudy skies the RMS differences were 13.6 per cent of the mean for daily totals; and 4.2 per cent of the mean for monthly averages. Monthly statistics are presented as average monthly cloudless irradiance, average monthly cloudy irradiance and a 'worst case' monthly irradiance. Considerable interannual variability is observed in the 'worst case' monthly irradiance. Depletion by clouds is very significant and is larger than interannual variability in ozone depletion. The effect of clouds is minimum at 55°S and increases polewards to reach maximum values at the edge of the pack ice. Further to the south, cloud depletion decreases due to the moderating effect of the high surface albedo for snow and ice. © 1997 by the Royal Meteorological Society.