Study of solar irradiance at high southern latitudes over a decadal time scale.

摘要

Long-term measurements of ground-level solar irradiance are necessary to fully understand the effects of ultraviolet radiation on ecosystems. Comprehensive data spanning over a decade are now available for specific locations. This study utilizes ground-level solar radiation data at four high-southern-latitude sites, being Ushuaia, Palmer station, McMurdo station, and the South Pole, from low to high latitude, respectively. The behavior of surface solar radiation, especially at ultraviolet wavelengths, is examined.; The data contain an upward trend in erythemal irradiance during November and December at the two highest-latitude stations over the 12-year period. The results also show a sign of longer-duration ozone depletion during the austral springs.; Of the several wavelength bands and biological weightings available, the DNA-weighted irradiance shows the biggest interannual variability. Furthermore, Ushuaia is the station with least interannual variability among the four sites.; Based on the climatological values of the DNA weighted irradiance and the ratio of DNA to UVA₂, changes in column ozone have been sufficiently large to distort the character of the annual cycle in the ultraviolet irradiance. During the decade of the 1990s, October and November replaced December as the months of maximum weighted irradiance or DNA to UVA₂ ratios.; Column ozone and clouds are two independent factors that affect surface ultraviolet irradiation. In some cases, these two effects can reinforce each other. For example, in October 1991 at Palmer station, the clear sky erythemal irradiances in October exceeded those for November; with clouds, the measured erythemal irradiance for October even exceeded that for December.; We used clear-sky irradiances computed from a radiative transfer model as the independent variable in a regression model designed to explain the variability in the measured irradiances. The calculation used column ozone measured by satellite. The measured UVA₂ irradiance was a second independent variable, selected because of its sensitivity to cloudiness. The multiple regression model can explain up to 99% of the observed variance in irradiance at the South Pole. The poorest-quality regression was at Ushuaia, where the model explained only 68% of the variance in measured irradiance.