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Results and Discussion

Relative UV-B and ozone deviations were calculated using as reference values the maximum total ozone in the period and the UV-B intensity corresponding to the day of maximum ozone.

Figures 1, 2, 3 and 4 show  UV-B and ozone anticorrelations.

Figure 1: maximum daily UV-B for Punta Arenas, at left with all data; at right with the removal of cloud effects. Upper panel, UV at 305 nm, middle panel, UV at 325 nm, lower panel, UV ratio 305/325 nm.

Fig.1  - Ozone and UV-B anticorrelations at Punta Arenas maximum daily UV-B.

Figure 2: UV-B at solar zenith angle (sza ) = 55^o for Punta Arenas, at left with all data; at right with the removal of cloud effects. Upper panel, UV at 305 nm, middle panel, UV at 325 nm, lower panel, UV ratio 305/325 nm.

Figure 3: maximum daily UV-B for Cuiabá, at left with all data; at right with the removal of cloud effects. Upper panel, UV at 305 nm, middle panel, UV at 325 nm, lower panel, UV  ratio 305/325 nm.

Figure 4: UV-B at solar zenith angle (sza ) = 45^o for Cuiabá, at left with all data; at right with the removal of cloud effects. Upper panel, UV at 305 nm, middle panel, UV at 325 nm, lower panel, UV ratio 305/325 nm.

Fig.4  - Ozone and UV-B anticorrelations at Cuiabá, UV-B at sza=45^o.

The anti-correlation studies were made by using ozone daily average data, and measured UV-B radiation: the maximum daily value, and the observation at a fixed solar zenith angle. Spectral irradiance at two wavelengths, 305 nm with strong ozone absorption and 325 nm, with very weak ozone absorption, were used, and the irradiance ratio 305/325 was obtained in order to eliminate the noise effect of clouds. Four data sets were used: maximum daily with all data, maximum daily without cloudy days, measurements at a fixed solar zenith angle, and measurements at a fixed solar zenith angle with cloudiness removed. It was observed that at both stations spectral maximum UV-B values show very low correlation coefficients with total ozone, and only the irradiance ratio has a more significant correlation coefficient. It is only when the geometry sun-observer is removed that the correlations show. The measurements at a fixed solar zenith angle show much higher correlations. For example, the correlation coefficients for the signal ratio 305/325nm with the removal of cloudiness, and using the daily maxima, are only 0.05 for Cuiaba, and 0.14 for Punta Arenas; whereas for a fixed solar zenith angle, the correlations are 0.61 for Cuiaba, and 0.79 for Punta Arenas.