Prolonged enhancement in surface ultraviolet radiation during the Antarctic spring of 1990

Measurements of the ultraviolet solar spectral irradiance from the earth's surface at Palmer Station, Antarctica, latitude 64.8 degrees South, show behavior in the spring of 1990 which differs from that observed during the seasonal ozone depletions of the previous two years. As the Austral spring progresses, the sun rises in the sky, and the duration of daylight increases up to the summer solstice on December 21. This is naturally accompanied by increasing ultraviolet irradiances irrespective of the behavior of column ozone. If, as in 1988, the ozone depletion is confined to October and early November, the irradiances at local noon may remain at or below values characteristic of an unperturbed summer solstice. However, in 1990 enhanced irradiances persisted well into December. The largest values observed at a wavelength of 306.5 nm were approximately double those expected at summer solstice with an unperturbed ozone amount.