• Introduction
• Instrumentation
• Results and Discussion
• Conclusions
• References

FIGURES

• Figure 1
• Figure 2
• Figure 3
• Figure 4

A simple correlation study using daily average ozone variables and UV-B daily maximum values shows very low if not complete absence of any correlation. This is found for both low and high latitude data. The expected anticorrelations can be revealed, however, when the variables are obtained at a fixed solar zenith angle, and when the noise in the data, especially that caused by clouds, is decreased or removed. Results for the stations Cuiaba (15^oS, 56^oW) and Punta Arenas (53.2^oS, 70.9^oW) show significant increases in the correlation coefficients for the wavelength where ozone is strongly absorbing.

Introduction

Ozone and UV-B anticorrelations have been studied in recent years(McKenzie etal., 1991; Bais et al., 1993; Kerr and McElroy, 1993; Bojkov et al., 1995; Herman et al., 1996)with the aim to determine by how much UV-B could increase due to global ozone depletion (Herman et al., 1993). In this work,an anticorrelation study is made at two south american stations, one at low latitude, Cuiabá (15^o S, 56^o W) and one at a relatively higher latitude, Punta Arenas, (53.2^o S, 70.9^o W).

Instrumentation

In this work UV-B radiation (280-320 nm) and ozone data from Brewer spetrophotomers are used. These spectrophotometers have been operated by INPE – the National Institute for Space Research of Brazil, since 1991 at Cuiabá and 1992 at Punta Arenas (Kirchhoff etal., 1993; Kirchhoff et al., 1997). A full year of data, 1995, was used to anticorrelation study.

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 showUV-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, UVratio 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.

Conclusions

UV-B and ozone anticorrelations were studied using Cuiaba and Punta Arenas data for the entire year of 1995. It was shown that maximum UV-B radiation shows poor or no anticorrelation with total ozone. Only by using UV-B radiation at a given solar zenith angle is that the ozone and UV-B relation became more visible. Eliminating the cloud influence and using the irradiance ratio 305/325 helps to improve the correlation. It was observed,forirradiance ratio, the correlation coefficients r² increased from 0.20 and0.10 (maximum UV-B, Punta Arenas and Cuiabá) to0.79 and 0.61 (cloud effect removed, UV-B atsza = 55^o,Punta Arenas, and at sza = 45^o, Cuiabá).

References

Bais, A. F., C. S. Zerefos, C. Meleti, I. C. Ziomas, and K. Tourpali, Spectral measurements of solar UVB radiation and its relations to total ozone, SO₂ and clouds, J. Geophys. Res., 98, 5199-5204, 1993.

Bojkov, R. D., V. E. Fioletov and S. B. Diaz, The relationship between solar UV irradiance and total ozone from observations over southern Argentina, Geophys. Res. Lett., 22, 1249-1252, 1995.

Herman, J. R., R. McPeters and D. Larko, Ozone depletion at northern and      southern latitudes derived from January 1979 to December 1991 Total Ozone Mapping Spectrometer data, J. Geophys. Res., 98, 12783-12793, 1993.

Herman, J. R., P. K. Bhartia, J. Ziemke, Z. Ahmad and D. Larko, UV-B increases (1979-1992) from decreases in total ozone, Geophys. Res. Lett., 23, 2117-2120, 1996.

Kerr, J. B.; McElroy, C. T.Evidence for large upward trends of Ultraviolet-B radiation linked to ozone depletion.Science, 262, 1032-1034, 1993.

Kirchhoff, V. W. J. H.;Alves, J. R.;Silva, F. R.;Motta, A. G.;Chagas, J. R.; Valderrama, V.; Zamorano, F.; Casiccia, C.The brazilian network of stratospheric ozone monitors: Observations of the 1992 ozone hole.Rev. Bras. Geofís.,11, 205–214, 1993.

Kirchhoff, V.W.J.H., Casiccia S, C.A.R., and Zamorano B, F., The Ozone Hole over Punta Arenas, Chile, J. Geophys. Res., 102, 8945-8953, 1997.

McKenzie, R.L., W.A.Mathews, and P.V.Johnston, The relationship between erythemal UV and ozone derived from spectral irradiance measurements, Geophys.Res.Lett., 18, 2269-2272, 1991.