Figure 1.

Ozone depletion and springtime UV levels over Ushuaia. (A) Increase in the number of ozone-hole days over Ushuaia during the past 2 decades. The graph shows the number of days with column ozone values ≤250 DU between Oct. 1 and Nov. 30 for each year. Data were obtained from the Overpass Data file on the internet TOMS site (http://jwocky.gsfc.nasa.gov/TOMSmain.html). No data are available for 1995, and a limited data set is available for October 1993; therefore, these two years are not included in the graph. (B–F) Effects of the passage of the Antarctic ozone hole over Tierra del Fuego on ground-level UV doses during October and November 1997. The spectral irradiances obtained by the National Science Foundation scanning spectroradiometer were converted into effective irradiances by using several weighting functions and integrated over the 9:00–13:30 h time period (■, effective UV dose; ▴, ozone column in Dobson units). The r² values shown in each panel are from a multiple linear regression model that incorporated Julian day and ozone level as independent variables; in all cases, the ozone term was statistically significant. A comparison of the Erythema-weighted UV doses calculated from spectral irradiance data in Ushuaia with those measured in the field site with a broad-band UV detector (Solar Light, Philadelphia, model PMA2102) indicated a significant linear correlation (r² = 0.77; 22 data points; November 1997; integration period 9:30–13:30 h).