Behavior of solar ultraviolet irradiance at high southern latitudes over a decadal timescale

摘要

Continuous measurements of solar ultraviolet spectral irradiance exist for four sites in the high latitude Southern Hemisphere, from 55°to 90 °S, and span a time period in excess of a decade. This database allows comprehensive analyses of variability in ground-level radiation over a wide range of time scales. The behavior of irradiances within a single month reflects the combined influences of changing solar elevations, cloudiness and ozone amounts. Histograms assembled for corresponding months over the decadal time scale reveal maximum instantaneous irradiances that can vary by a factor of two or more among different years. An important portion of each year encompasses the months from October through December. The annual ozone loss develops during this period, and in some years this is sufficiently dramatic to distort the seasonal cycle in erythemal irradiance expected solely on the basis of solar elevation. Under unperturbed conditions, the largest monthly-integrated irradiances would occur in December at all wavelengths from 290 to 400 nm. However, in years of unusually low springtime ozone amounts the maximum monthly-integrated erythemal irradiances can appear in November.