Recent Submissions

  • Influence of mesoscale atmospheric forcing on mean sea level at Piraquara, RJ

    Uaissone, A.J.R.; Universidade Federal do Rio de Janeiro (2004)
    The work refers to variations of the mean sea level (MSL) in Piraquara (RJ) due to mesoscale atmospheric disturbances in the South and Southeast Brazil oceanic area. The sea level data were submitted to a verification and consistence process, and then they were validated with the help of predicted levels by the software Pacmaré (FRANCO, 1992). For the pressure and wind velocities, the NCEP re-analysis data was used. Thompson's low pass optimizable filter was used to remove high frequencies in the data. Differently to the habitual use of quarters of year in climatologic studies, in this work partitions of the year centered in solstice and equinox were considered. About the results of the statistical analysis in the time domain, it was seen that MSL response has time delays with respect to atmospheric pressure and wind stress. The spectral analysis, in the frequency domain showed that during the equinox centered days the high peaks of energy are in relatively lower frequencies than in the solstice period, and they appear in the same frequency band as that of the cold fronts. Pressure points under continental influences present little coherent with the MSL variations in Piraquara, on the other hand, the effects of the longitudinal component to the coast are very well-known on the mean sea level. It is proposed to study the subtropical anticyclone in the South Atlantic Ocean in order to identify probable phenomena that explain the occurrence of high energy picks in low frequencies, as well as identify types of cold fronts which reach South and Southeast regions of Brazil, since they have diferente impacts on the coastal region.
  • Hydrodynamic numerical modelling of Maputo Bay

    Canhanga, S.J.V.; Aveiro : Universidade de Aveiro (2003)
    The aim of this work was to understand by using a numerical model, the main characteristics of the Maputo Bay hydrodynamics; and furthermore to assess the hydrodynamics implications on the different processes that can occur in the Bay. The study was initiated with a description of the hydrodynamical characteristics of Maputo Bay, through the analysis of vertical profiles of salinity and temperature, time series of the components of tide currents and water elevation. The wind intensity and river runoff patterns were also studied. Analysis of temperature and salinity profiles have revealed that the Maputo Bay can be considered vertically homogeneous; however, when floods occur or when there is high intensity of precipitation on summer season, a horizontal stratification of salinity and temperature in Maputo Bay was observed. The tides were identified as the main forcing on the Maputo Bay hydrodynamics. The general patterns of other forcing (winds and river discharges) were also identified. Through the characteristics of the Bay (vertically homogeneous), and the process that is intended to be understood (long wave propagation), a bidimensional numerical model SYMS/S2D was chosen as the best to perform this study. Afterwards, the model was calibrated by comparison of observed and simulated time series of tide elevation, the horizontal and the vertical components of tidal currents. Results of calibration have shown that the model reproduces with accuracy the wave propagation in the Bay. The hydrodynamic study allows the determination of the form number (type of tide); the amplitude and phase of the main constituents, as well as, the influence of non-periodic forces on the Bay hydrodynamics, through the determination of residual currents. The results of the hydrodynamic model have shown that in the Maputo Bay, the tide is essentially semi-diurnal, and that the main semidiurnal constituents, M2 and S2, represented almost 90% of the total astronomical tides. In most part of the Bay, the tidal wave has exhibited a characteristic that lies between a standing and a progressive wave. Was also noticed by the results of the Eulerian residual circulation, that the influences of rivers, winds and bathymetry on non-periodic forces were very important on long-term processes. A Langrangian module was also coupled to the hydrodynamic model, to assess the evolution of dispersion processes of passive particles in the Bay. The results of the angrangian module have shown that for time scales superior than a tidal cycle, the mixing and dispersion processes are more important in the central part of the Bay and in the Estuário spírito Santo zone, respectively; in other zones these values are actually insignificants. The range of flushing time in the Estuário Espírito Santo zone lied between on day (on the mouth of the estuary).