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Long-term measurements of total ozone have been carried out by The National Institute for Space Research, INPE, at Natal (5.8^oS, 35.2^oW) and C. Paulista (23.1^oS,45W), since 1978 and 1974, respectively, using two Dobson spectrophotometers. A spectral analysis was applied on these time series, using the Multiple Taper Method, the Maximum Entropy Spectral Analysis and an Iterative Regression Model. The time series were the yearly averages, 12 months (12m) and  36 months (36m) running means, and 12m-36m time series. Using these time series, the main periodicities found were 2.45 and 10 years for Natal, and 2.45 and 8 years for C. Paulista, associated to the quasi-biennial oscillation (QBO) and to the 11 year solar cycle. The amplitudes of these periodicities were close to 1% of the averages. Using 36m the QBO signal was eliminated (r² = 0.01 between total ozone and the zonal wind index, for Natal) and the solar cycle signal could be more easily seen. It was observed that ozone at Natal has a variation in-phase with the sunspot number, while at C. Paulista an out-of-phase variation was observed, with a lead for ozone of about 2 years. To study the QBO signal  the difference between 12m and 36m time series was calculated, removing the longer periods. In this time series, the correlation between total ozone and zonal wind index was higher, positive at Natal and negative at Cachoeira Paulista

Introduction

The solar cycle on total ozone is about 1-2% per cycle, and ozone varies in phase with the sunspot number (Ruderman and Chamberlain, 1976; Brasseur and Solomon, 1986; Zerefos et al., 1997). The Quasi-Biennial Oscillation ­ QBO, was identified in ozone as related to the zonal wind oscillation of 26-30 months ((Funk and Graham, 1962), and it is in phase with the zonal wind at equatorial regions and has a variation out-of-phase in extratropical latitudes (Hilsenrath and Schlesinger, 1981; Zerefos et al., 1992; Hollandsworth et al., 1995; Kane et al., 1998).

Long-term measurements of total ozone have been carried out by The National Institute for Space Research, INPE, at Natal (5.8^oS, 35.2^oW) and Cachoeira (C.) Paulista (23.1^oS,45W), since 1978 and 1974, respectively, using two Dobson spectrophotometers. In this paper a spectral analisys is made on Dobson ozone data to study the solar cycle and the QBO signal on total ozone in these two tropical stations. In Table 1 are shown the geographical locations of the stations and the period of the data analyzed.

Table 1: Observational sites