Solar irradiances over Ushuaia (54.49° S, 68.19° W) and San Diego (32.45° N, 117.11° W) geographical and seasonal variation

The study of long-term variability in UV-B irradiance in places affected by the "ozone hole" and the comparison with undisturbed places is of interest for the atmospheric community, and is also useful from the biological and epidemiological points of view. Since some ecosystems are also sensitive to other bands of the solar spectrum, the study of UV-A and visible are also of interest. In this paper, we compare the irradiance in the UV-B, UV-A and visible at Ushuaia (54.49 degrees S, 68.19 degrees W) and San Diego (32.45 degrees N, 117.11 degrees W), going from instantaneous to year-integrated values. As some ecosystems are sensitive not only to the absolute value, but also to the relative changes, we also analyse the ozone and irradiance relative variations. The large variability in the total ozone column at Ushuaia combined with other parameters such as solar zenith angles, cloud cover and amount of daylight hours results in a wide variety of situations. For the ozone-sensitive bands, peaks of daily and daily-integrated maximum irradiance observed at Ushuaia during spring are remarkably higher than expected, although seldom reaching the maximum observed at San Diego. For the UV-A and visible, values at Ushuaia during the late spring and summer are very close to and, in a few cases, even exceed those at San Diego. The highest monthly integrated irradiance for the band 298.507-303.030 nm, at Ushuaia, was observed in December 1990, with a value well above the mean for that month. Relative ozone variation at Ushuaia presents the most important depletion and largest dispersion during the spring, as expected. While, for the ozone-sensitive bands, the largest relative irradiance increment is observed during the winter. (C) 2001 Elsevier Science Ltd. All rights reserved.