Application of a simple model to calculate latitudinal and hemispheric differences in ultraviolet radiation
A simple model to calculate the clear-sky global ultraviolet (UV) irradiance received on a horizontal surface is introduced and validated against absolute spectral UV irradiance measurements made during a short campaign at Lauder, New Zealand (45°S, 170°E). The model is used to investigate the latitudinal and seasonal variations of UV irradiance at 298, 302.5, 307 and 340 nm, using a climatology of zonally averaged satellite ozone measurements made over a 4 year period from 1979 to 1982. The calculations show strong seasonal and latitudinal variations, particularly at the shorter wavelengths. Compared with similar latitudes in the Northern Hemisphere, UV irradiances in the Southern Hemisphere are relatively high. The differences are due to (1) the closer Sun-Earth separation, and (2) the lower ozone amounts, in the Southern Hemisphere summer compared with the Northern Hemisphere summer. In unpolluted conditions the peak monthly fluxes (midday, summer) at 307 nm are 13% more at midsouthern latitudes than at comparable northern latitudes: they are equivalent to those in the Northern Hemisphere at latitudes 5° closer to the equator. The asymmetry is more pronounced at shorter wavelengths. When likely hemispheric difference in turbidity are considered, the hemispheric asymmetries are amplified. Further amplifications can also be expected from the development of the Antarctic ozone hole.