João Antônio Lorenzzetti

A numerical study of the effects of bottom topography and coastline geometry on the Southeast Brazilian coastal upwelling

Abstract A two-layer finite element model is used to investigate the effects of bottom topography and coastline geometry on the coastal upwelling of the Southeast Brazilian continental shelf. Three cases are analyzed: (1) real topography and real coastline; (2) flat bottom and real coastline and (3) real topography and smoothed coastline. For all the numerical simulations the model was integrated for five days using a constant northeast wind. The first case reproduces reasonably well the characteristics of wind-driven upwelling with respect to location and magnitude. When comparing the second and third case results with the first one, it can be seen that local bottom topography and coastline geometry affect the upwelling magnitude in the whole domain. The coastline irregularities are important in the location of the upwelling cores in the south portion, which extends from Cabo de Sao Tome to Rio de Janeiro, primarily near Cabo Frio. Moreover bottom topography seems to be responsible for the location of the upwelling cell in the north portion of the domain, from Cabo de Sao Tome to Vitoria. In contrast to previous findings, the coastline irregularities are found to dominate over topographic variations in determining the location of Cabo Frio coastal upwelling.

The response of the South Brazil Bight to the passage of wintertime cold fronts

On the southeastern continental shelf of Brazil the wintertime subtidal variability of the circulation is highly dominated by the passage of cold fronts. Hydrographic data for the region reveal that during this (July, August, September) season only a weak vertical stratification is observed. In this paper the response of the region to cold fronts is studied by using a barotropic finite element model, forced by a conceptual cold front wind field derived from the analysis of coastal winds and satellite imagery.

Telemetric monitoring system for meteorological and limnological data acquisition

(2006). Telemetric monitoring system for meteorological and limnological data acquisition. SIL Proceedings, 1922-2010: Vol. 29, No. 4, pp. 1747-1750.

Ship Detection Using TerraSAR-X Images in the Campos Basin (Brazil)

The very large extent of the Brazilian coast (~8000 km) and the growing maritime vessel traffic demand that research be made on ancillary methods to monitor and control ships traffic in national waters. An important tool for this purpose is the use of orbital synthetic aperture radar (SAR) imagery, particularly due to its ability to work day and night and to suffer almost no interference of cloud coverage. In this letter, we investigate some ship detection concepts, as applied to TerraSAR-X (TSX) ScanSAR images (16-m resolution), in VV and HH polarization. Ocean clutter statistical parameters are estimated, and the Kolmogorov-Smirnov test is used to verify the goodness of fit for the K-distribution to TSX images. A constant false alarm rate (CFAR) target detection algorithm is developed, and its performance is verified. Incidence angle, CFARs window size, and probability of false alarm influence are further analyzed.

Assessment of Spatial Interpolation Methods to Map the Bathymetry of an Amazonian Hydroelectric Reservoir to Aid in Decision Making for Water Management

The generation of reliable information for improving the understanding of hydroelectric reservoir dynamics is fundamental for guiding decision-makers to implement best management practices. In this way, we assessed the performance of different interpolation algorithms to map the bathymetry of the Tucurui hydroelectric reservoir, located in the Brazilian Amazon, as an aid to manage and operate Amazonian reservoirs. We evaluated three different deterministic and one geostatistical algorithms. The performance of the algorithms was assessed through cross-validation and Monte Carlo Simulation. Finally, operational information was derived from the bathymetric grid with the best performance. The results showed that all interpolation methods were able to map important bathymetric features. The best performance was obtained with the geostatistical method (RMSE = 0.92 m). The information derived from the bathymetric map (e.g., the level-area and level-volume diagram and the three-dimensional grid) will allow for optimization of operational monitoring of the Tucurui hydroelectric reservoir as well as the development of three-dimensional modeling studies.

Multi-sensor synergistic analysis of mesoscale oceanic features: Campos Basin, south-eastern Brazil

This study presents a combined use of multi-sensor remote sensing and in situ data for the analysis and interpretation of oceanic features observed at the continental shelf and slope of the Campos Basin, south-eastern Brazil. Ocean colour (SeaWiFS), thermal infrared (AVHRR), scatterometer winds (QuikSCAT) and SAR (Radarsat-1) data were integrated to associate the different SAR backscatter patterns with physical and biological oceanic processes. The interpreted SAR features included processes such as oceanic fronts, current meandering and eddies, upwelling plumes, wind variability and algae blooms. The interpretation of these features was only feasible through the use of the multi-sensor synergistic approach complemented by timely field verification.

Swell and Wind-Sea Distributions over the Mid-Latitude and Tropical North Atlantic for the Period 2002–2008

We present an analysis of wind-sea and swell fields for mid-latitude and tropical Atlantic for the period 2002–2008 using a combination of satellite data (altimeter significant wave height and scatterometer surface winds) and model results (spectrum peak wave period and propagation direction). Results show a dominance of swell over wind-sea regimes throughout the year. A small but clear decrease in swell energy and an associated increase in wind-sea potential growth were observed in the NE trade winds zone. A seasonal summertime increase in wind-sea energy in the Amazon River mouth and adjacent shelf region and in African coast was apparent in the results, probably associated to a strengthening of the alongshore trade winds in these regions. Albeit with a significantly smaller energy contribution of wind-seas as compared to swell energy, we could say that a kind of mixed seas is more evident in the trade winds region, with the remaining area being highly dominated by swell energy. An analysis of wave-age shows the absence of young-seas. Only ~2% of all data points was classified as wind-sea, a classification confirmed by a fit to a theoretical relation between wind speed, peak period, and significant wave height for fully developed wind-seas.

A satellite view of riverine turbidity plumes on the NE-E Brazilian coastal zone

Turbidity plumes of Sao Francisco, Caravelas, Doce, and Paraiba do Sul river systems, located along the NE/E Brazilian coast, are analyzed for their dispersal patterns of Total Suspended Solids (TSS) concentration using Landsat images and a logarithmic algorithm proposed by Tassan (1987) to convert satellite reflectance values to TSS. The TSS results obtained were compared to in situ collected TSS data. The analysis of the satellite image data set revealed that each river system exhibits a distinct turbidity plume dispersal pattern. The behavior, dimension and degree of turbidity of the Sao Francisco River plume have been greatly altered by the construction of a cascade of hydroelectric dam reservoirs in its hydrological basin. The plume has lost its typical unimodal seasonal pattern of material dispersion and its turbidity has decreased due to the regulation of river flow by the dams and TSS retainance by the reservoirs. In contrast, the Doce and Paraiba do Sul river plumes are still subject to seasonal pulsations and show more turbid conditions than the SF plume, as dams are less numerous, set in the middle river sections and the natural river flow has been maintained. The Caravelas Coastal System river plume is restricted to near shore shallow waters dominated by resuspension processes. During austral spring and summer when NE-E winds prevail, all plumes generally disperse southward. Short-term northward reversals may occur in winter with the passage of atmospheric cold fronts. The Sao Francisco and Doce river plumes tend to disperse obliquely to the coast and transport materials further offshore, while the Caravelas and Paraiba do Sul plumes tend to disperse mainly parallel to the coast, enhancing TSS retention nearshore.

Simultaneous Measurements of Chlorophyll Concentration by Lidar, Fluorometry, above-Water Radiometry, and Ocean Color MODIS Images in the Southwestern Atlantic

Comparisons between in situ measurements of surface chlorophyll-a concentration (CHL) and ocean color remote sensing estimates were conducted during an oceanographic cruise on the Brazilian Southeastern continental shelf and slope, Southwestern South Atlantic. In situ values were based on fluorometry, above-water radiometry and lidar fluorosensor. Three empirical algorithms were used to estimate CHL from radiometric measurements: Ocean Chlorophyll 3 bands (OC3MRAD), Ocean Chlorophyll 4 bands (OC4v4RAD), and Ocean Chlorophyll 2 bands (OC2v4RAD). The satellite estimates of CHL were derived from data collected by the MODerate-resolution Imaging Spectroradiometer (MODIS) with a nominal 1.1 km resolution at nadir. Three algorithms were used to estimate chlorophyll concentrations from MODIS data: one empirical - OC3MSAT, and two semi-analytical - Garver, Siegel, Maritorena version 01 (GSM01SAT), and CarderSAT. In the present work, MODIS, lidar and in situ above-water radiometry and fluorometry are briefly described and the estimated values of chlorophyll retrieved by these techniques are compared. The chlorophyll concentration in the study area was in the range 0.01 to 0.2 mg/m3. In general, the empirical algorithms applied to the in situ radiometric and satellite data showed a tendency to overestimate CHL with a mean difference between estimated and measured values of as much as 0.17 mg/m3 (OC2v4RAD). The semi-analytical GSM01 algorithm applied to MODIS data performed better (rmse 0.28, rmse-L 0.08, mean diff. -0.01 mg/m3) than the Carder and the empirical OC3M algorithms (rmse 1.14 and 0.36, rmse-L 0.34 and 0.11, mean diff. 0.17 and 0.02 mg/m3, respectively). We find that rmsd values between MODIS relative to the in situ radiometric measurements are < 26%, i.e., there is a trend towards overestimation of RRS by MODIS for the stations considered in this work. Other authors have already reported over and under estimation of MODIS remotely sensed reflectance due to several errors in the bio-optical algorithm performance, in the satellite sensor calibration, and in the atmospheric-correction algorithm.

Mean diel variability of surface energy fluxes over Manso Reservoir

Abstract Mean diel cycle of latent (E), sensible (H), net longwave (Lwnet), net shortwave (Sw), and net surface heat flux balance (S) were estimated from hourly meteorological and subsurface water temperature time series acquired for ~1 month during mid-austral autumn by a buoy system in a large tropical reservoir in Brazil. E and H were in phase and had their maximum (E = 163 Wm−2; H = 39 Wm−2) at early morning and minimum (E = 112 Wm−2; H = 6 Wm−2) midafter-noon, resulting in Bowen ratios of 0.24 and 0.06, respectively. Heat loss by evaporation therefore dominates over sensible heat used to warm surface atmosphere. Atmospheric instability was present almost all the time, increasing latent and sensible heat flux exchange coefficients by ~50% over their neutral values (from 1.4 × 10−3 to 2.2 × 10−3). Mean Lwnet varied from 76 at late afternoon to 89 Wm−2 at early morning, indicating its importance in the overall surface heat flux balance. All 3 fluxes (E, H, and Lwnet) were positive (reservoir losing energy) throughout the day. The integrated daily average net energy budget S (net short wave radiation minus E + H + Lwnet) was ~ −60 Wm−2; nighttime energy loss exceeded daytime gain, with consequent cooling of the reservoir. A mean temperature drop of about −0.1 °C d−1 was obtained by fitting a linear trend line to observed daily mean surface temperatures. In a qualitative way, diel time variations of surface water temperature were consistent to the time variability of S, indicating the dominant role of the surface heat budget in modulating surface layer temperatures of the reservoir.