ULTRAVIOLET-RADIATION AT SITES ON THE ANTARCTIC COAST

Ground-based measurements of solar UV irradiance combined with calcula tions using satellite-based ozone data are able to define the variabil ity in UV sunlight at Palmer Station and McMurdo Station, Antarctica o ver time scales of years. Special attention focuses on the spring and summer seasons. Satellite data show that the annual ozone loss that oc curs during October was greater in 1991-1992 than in 1979-1980, This l ed to average noontime UVB irradiances computed for clear skies in the latter period that exceeded those in the earlier time by 50-65%, Howe ver, a biologically weighted irradiance for suppression of photosynthe sis in phytoplankton indigenous to the area near McMurdo Station incre ased by at most 5% over this period in response to the change in ozone owing to an important contribution from the UVA, At Palmer Station th e behavior of ozone and cloudiness can mesh so as to produce the large st noontime UVB irradiances of the year in October as opposed to near summer solstice in December and January. Interannual variability in UV B irradiance during October, the month of the major ozone loss, is lar ger at Palmer than at McMurdo during the time spanned by ground-based irradiance measurements, being 1990-1994. However, interannual variati ons in cloudiness were more important than changes in ozone in causing the observed year-to-year variability at Palmer Station, The opposite situation prevailed at McMurdo during October, where interannual vari ations in ozone were responsible for most of the year-to-year differen ces in UVB received at the ground.