Afranio Rubens de MESQUITA; Joseph HARARI & Carlos Augusto de Sampaio FRANÇA

Instituto Oceanográfico da Universidade de São Paulo (IOUSP)

Introduction

Sea surface Temperature series, atmospheric pressure series, series of coral growth are reported to be the record of variations almost periodical with scales of decades and interdecades for long periods of observation reaching 300 years before present. In Brazil the series of atmospheric precipitation of Fortaleza, Ceará State, with almost 140 years of length also record statistically significant oscillations with periods of the same order. The same time scales were also found to occur in the South-eastern coast of Brazil (Mesquita & Morettin, 1984).

Results

Results of the investigation are shown in Figure 1 (Mesquita et al., 1995) where the periodogramme of the series of sea level of San Francisco USA and the periodogramme of the series of atmospheric precipitation of Fortaleza are displaced. It noticeable the occurrence of the decadal and interdecadal time scales in both periodogrammes. The sea level data from Cananéia produced a spectrum of the smoothed autocovariance function shown in Figure 2. There it can also be seen the occurrence of the same scales of variability with 95% of statistical significance level, such as those bands centred at 23 years, 3.3 years, 5.5 years (not significant) and 12 to 13 years, all of them with as 10 cm order of magnitude. Other oscillations also appearing in the spectrum are centred in the spectral bands of 5.3 months caused by the oceanography of the South Atlantic, those of 6 months and 12 to 13 months related to the Earth's orbit and other related to the Chandler Wobble, Melchior (1980), with bands round 14 and 16 months.

Fig. 1. Periodograms of rainfall of Fortaleza series of Ceará, Brazil (top) and the sea level of San Francisco, USA (bottom).

The correspondence between the spectra shown in Figures 1 and 2 is also corroborated by scales of the spectra of Coral growth of the Pacific, Dunbar & Cole (1993), as well as with time scales determined by the spectra of global fluxes of the great rivers all around the globe produce by Kayser et al. (1990).

Fig. 2. Spectrum of sea level of Cananéia State of Sao Paulo, 432 monthly sea level values, 1955 to 1990.

Possible causes for the variability in Southern coast of Brazil, where the port of Cananéia is located, are related to the ENSO phenomena as the same scales are also observed in the Sea level of San Francisco, USA. They seem to be all related to ENSO as its geographical scales are such to embrace both localities. The causes of the ENSO themselves are not known and the speculations indicate the seismicity of the Pacific as a possible cause and the susnspots that also have the same spectral bands that may be responsible for them. (Morettin et al., 1993).

Conclusions

From these arguments it seems evident that a phenomena with time scales of decades and interdecades influence the sea level of the town of Cananéia and that these scales are correspondent to those of phenomena of ENSO, that may be causing these scales of variability in the entire coast of Southern Brazil, where Cananéia is located.

References

Dunbar, R. B. & Cole, J. E. 1993. Coral records of Ocean-Atmosphere variability. Report of the Workshop on Coral Paleoclimate reconstruction. National Oceanic and Atmospheric Administration Special Report, 10:1-38.

Kayser, N. Probst, J. L. Cadet, D. & Tardy, I. 1990. Propagation des ondes de sicheresse et dquote humiditi quote  travers le monde. C. r. Acad. Sci., Paris, t. 310, sirie II, p 757-763.

Melchior, P. 1980. For a clear terminology in the polar motion investigations. In: Federov, E. P.; Smith, M. L.quote  & Blender, P. eds Nutation and Earthquote s rotation. Int. astr. union Symposium. Kiev 23-28 May 78. D Riegal Publishing Co., London, p. 17-20.

Mesquita, A. R. de & Morettin, P. A. 1984. Interannual variation of precipitation in Ceará, Brazil. Tropical Ocean-Atmosphere Newsletter. NOAA, 27:9-10.

______; Harari, J. & França, C. A. S. 1995. Interannual variability of tides and sea level at Cananéia Brazil, from 1955 to 1990. Publicação esp. Inst. oceanogr., Univ. S Paulo, (11):11-20.

Morettin, P. A.; Toloi C.; Gait, N. & Mesquita, A. R. de 1993. Analysis of the relationship between some natural phenomena: atmospheric precipitation, mean sea level and sunspots. Revista Brasileira de Meteorologia, 8(1):11-21.