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Master's Dissertation
DOI
10.11606/D.21.1994.tde-19032009-153439
Document
Author
Full name
Marco Antonio Correa
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1994
Supervisor
Committee
Morettin, Pedro Alberto (President)
Dias, Pedro Leite da Silva
Lorenzzetti, João Antonio
Title in Portuguese
ANÁLISE DAS OSCILAÇÕES DAS CORRENTES OBSERVADAS NA BAÍA DE ILHA GRANDE (RJ).
Keywords in Portuguese
análise de séries temporais
análise do ruido branco
análise espectral cruzeda
baía da Ilha Grande
espectros rotatórios
Seiches
Abstract in Portuguese
Series temporais de correntes, vento (força e direção), temperatura e salinidade, com duração de 24h, obtidas em 5 estações na Baia da Ilha Grande (rj), de 3-29/01/82, foram analisadas. As medições de corrente foram feitas a5, 12 e 20m, a cada 5min e a 2m acima do fundo, a cada 12min; temperatura e salinidade em cinco profundidades a cada 3h e vento a cada 1h. Foram utilizadas análises de series temporais através dos métodos diretos (periodograma) e indireto para as estimativas espectrais alisadas, bem como as equações hidrodinâmicas na determinação dos períodos. Foram utilizados os testes: ruído branco e fisher-whittle, a análise dos espectros rotatórios e a análise cruzada entre vento e corrente, ao longo de três camadas: superfície intermediaria e de fundo. Foram determinadas oscilações de 4,8h e identificadas como seiches internos e detectadas oscilações com período de 3,4h associadas à ressonância com o vento. Em todo o sistema da baia o período de 6h mostrou-se significativo, correspondendo à oscilação natural da baia. Foram detectadas oscilações de alta freqüência 11 e 20min, 20cm/s eventualmente associadas a vórtices e meandros da corrente. Água subtropical na camada de fundo da baia
Title in English
Analysis of the current oscillations observed at Ilha Grande Bay (RJ)
Keywords in English
cross spectral analysis
Ilha Grande Bay.
rotary spectra
Seiches
time-series analysis
white noise analysis
Abstract in English
Temporal series of currents, wind, water temperature and salinity, obtained from 5 oceanographic stations located in and around Ilha Grande Bay (RJ, Brazil), from January 23 to 29, 1982, were analyzed. AlI series have 24 hours. Currents measu¬rements were dione at depths of 5, 12, 20 m (every 5 minutes) and near the bottom (every 12 minutes). Temperature and salinity data were taken from 5 depths every 3 hours for each, while the wind was measured every hour. The present work was per¬formed in order to investigate short-period oscillations present in the region, related to density stratification and to the features of the basin, as well as to describe the circulation patterns and currents variations during one day interval. Two kinds of analysis were used: temporal series analysis, using statistical and spectral methods, and calculations by hydrodynamic motion equations. In temporal series analysis the direct (periodogram) and indirect methods were used for the spectral estimations. White-noise, Fisher- Whittle tests and rotational spectra analysis were also applied, besides the cross spectrum analysis for the data about winds and currents. The results indicate an intense and unidirectional circulation in the layer above 5 meters, from the western to the eastern portion of the Bay, through Central Channel. In this layer, on the eastern sea-opening side, a flux toward the Bay was observed. These motions, within 5 meters depth, were attributed to a circulation generated by a horizontal density difference between oceanic and inshore waters, with few contribution from tides and winds. At intermediate and near bottom layers, a horizontal homogeneity was observed and, consequent1y, smaller horizontal density gradients were detected. This way, circulation caused by tides was stronger than the movements forced by su¬perficial layers. Resultant bottom currents, observed at the Bay openings, led to the open-sea. At Central Channel, 4.8 h period oscillations were detected, and identified as internal seiches. In the eastern Portion, 3.4 hour period oscillations were detected, related to wind resonance. In alI the bay-system, the 6.0 hour period was significant, corresponding to the bay's natural oscillation. The study area presented a density stratification in two layers, with a single water type filling alI the portion below the 20 meters. This water, with characteristics of Subtropical Water, occupied the bottom layer due to an upwelling process produced by the dynamics of currents and winds in the continental shelf . In the two stations located off the bay, the wind and currents observations support this upwelling hypothesis.
 
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Publishing Date
2009-03-25
 
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