Jose Antonio Moreira Lima

Reconstituição do clima de ondas no sul-sudeste brasileiro entre 1997 e 2005

A criterious hindcasting study of the South Atlantic Ocean wave field was made using the model WAVEWATCH III including tests to evaluate which numerical grid would provide the best configuration for the wind and other atmospherics forcing regarding the calibration of the respective fields. It was observed that the wind forcing values were slightly underestimated for speeds below 7.5 m/s and overestimated for speeds above this value for specific sites at Campos and Santos Basins (Brazil). Thus, it was proposed a small correction to compensate any trends in the wind forcing values for the region. The evaluation of resultant wave fields was made using extreme measured sea states at PETROBRAS platform P-25, northern Campos Basin. The comparison of measured and modeled values shows that the adjusted atmospherics forcing provided good results for both significant wave heights (Hs) as well as spectral peak periods (Tp). Although, it was observed that the modeled sea states tend to slightly underestimate the local sea component at the initial storm buildup when a second spectral peak is present. It was also observed that the used numerical grid tends not to capture very compact atmospheric systems due to poor resolution of such small scale features. On a general view, the results reproduce the wave field characteristics of the western South Atlantic Ocean.

Modelo paramétrico analítico para a estrutura de velocidade do sistema corrente do Brasil

Velocity-based parametric models are often used in the oceanographic literature either in theoretical studies that involves linear stability properties or as boundary-initial conditions for regional implementations of numerical models. However, most of these models were developed for the Gulf Stream (Niiler & Robinson, 1967; Luther & Bane, 1985; Robinson et al., 1988; Arango et al., 1992; Xue & Mellor, 1993; Gangopadhyay et al., 1997). Because the Brazil Current (BC)- Intermediate Western Boundary Current (IWBC) System is unique in terms of its vertical structure as it flows off SE Brazil, an original parametric model has been developed and is presented in this paper. The model parameterizes both the surface-core structure of the BC as well as the intermediate level-core of the IWBC, keeping their basic features such as the asymmetric configuration due to their interaction with the topography. In the BC case, the model allows for the current shape to be deformed if it is close to the shelf break or to acquire a hyperbolic-like shape when it is positioned far away from the continental margin. In the IWBC parameterization, the main characteristic of the model is to reproduce a core placed at 800-900 m depth, adjacent to the intermediate portion of the continental slope. Additionally, under the assumption that the currents are in geostrophic balance, a sectional model of the density structure was obtained from the velocity model. This density model was constructed based on the integration of the thermal wind equation. Finally, the parametric model has been successfully tested, it reproduced with great accuracy the structure of three velocity sections obtained from observations within the boundaries of the so-called Campos Bight: 21oS, 22oS e 23oS.

Directional Extreme Current Profiles Based on Complex Empirical Orthogonal Functions (C-EOF) for Offshore Design

This paper presents a methodology to estimate deep water design current profiles using Complex Empirical Orthogonal Function (C-EOF) and a structural reliability response based model. The advantage of C-EOF is the capability of directly obtaining directional extreme current profiles. It is estimated that most of the variability of the southeast Brazil current system can be explained by the first two EOF modes. The first mode associated with the southwestward Brazil Current (BC) and the second mode with the northeastward Intermediate Western Boundary Current (IWBC). Thus, only two series of C-EOF amplitudes can be used in the response based technique to estimate the 100-y extreme current values. The methodology can also be used with more EOF modes if required to properly represent the current data. The probabilistic cumulative functions are based on extreme value distributions such as Gumbel or Weibull, and Lognormal for conditional distributions. The evaluation of estimated distribution parameters are carried out using Kolmogorov-Smirnov goodness-of-fit hypothesis tests and correlation coefficients for each directional sector.© 2009 ASME

DEEPWATER CURRENT PROFILE DATA SOURCES FOR RISER ENGINEERING OFFSHORE BRAZIL

A variety of current profile data sources are compared for a deepwater site offshore Brazil. These data were gathered for consideration as part of the Worldwide Approximations of Current Profiles (WACUP) Joint Industry Project, described separately in OMAE2012-83348. The primary source of data for current profile characterisation is site specific full water column measurement. Sufficiently high vertical and temporal resolutions are required to capture the dominant oceanographic processes. Such in-situ data are generally expensive and time consuming to collect, so there is an increasing tendency for numerical model current data to be considered for engineering applications. In addition to being relatively inexpensive and quick to obtain, model data are also typically of much longer duration. This potentially allows inter-annual variability and rare extreme events to be captured. However, the accuracy and reliability of numerical model data remains questionable, or unproven, in many deepwater development regions. This paper explores the suitability of such models to represent a deepwater site offshore Brazil, in relation to the key oceanographic processes revealed within the in-situ data.Copyright

Wave Measurements Using an Air Pressure Gauge

An equipment for wave and tide measurements using an air pressure gauge was developed and tested in a Brazilian coastal site (Ilha Grande Bay Maritime Terminal, Lat 23° 03’ 22” S/ Lon 44° 14’ 07” W) for 18 months. The main properties of this equipment were the low production costs and the improved maintenance procedures required by a dry sensor fixed over the sea water level. Data were analyzed using a standard Fast Fourier Transform (FFT) algorithm and the results were very good. As an example of the adequate spectral resolution attained with the analysis methodology, results from a bimodal sea state will be presented, the first peak with period of 5.43 seconds and the second one with a period of 8.30 seconds.Copyright

Investigating flow noise on underwater gliders acoustic data

Since November 2015, two underwater gliders equipped with external hydrophones were deployed in the South Brazilian Bight in order characterize the areas soundscape. Contrasting to standard fixed mooring systems (where flow noise is generated by currents passing by the hydrophones), gliders are subject to noise generated by its own downward and upward motion, which may compromise soundscape characterizations if not properly evaluated. In order to investigate induced flow noise on the hydrophone and its characteristics, 563 hours of acoustic data from the gliders were correlated to the navigation settings. Results can be comparable to previous flow noise descriptions for fixed systems. A high correlation was observed between the glider speed (both vertical and total) and 1/3 octave band levels centered at frequencies below 20 Hz. Estimates of the broadband sound pressure level were accomplished with different lower frequency limits and found to be uncorrelated to the glider speed above 40 Hz.

A Brazilian Northeast Coast Wave Data Comparison: Radar vs Buoy

Wave buoys are well known by its accuracy in measuring sea surface elevations while wave radars were developed later. Buoy’s motions are considered direct wave measurements while microwave radars use remote sensing for tracking the sea surface. Due to sensitivity to winds, sea surface roughness, rain, etc, it is a good practice to check radar data against buoys records. Even both systems installed being 6 km apart in a deep water region offshore northeast Brazilian shelf, there were differences in wave directional spectral parameters calculated by both equipments. The wave measurements at Sergipe and Alagoas basin were in good agreement in terms of significant wave height. Hs correlation was 91% and bias was only 0.06 m. A particular behavior of radar Hs when compared to buoy Hs was overestimation in high sea states and underestimation in low ones. Tp1 correlation was 69%, bias was 0.02 s and linear regression coefficient was 0.64. The worst correlated parameter was peak direction Dp1 with 60% of correlation for E-ESE directional band. Time series matched each other and showed the typical regional wave climate with Hs 1.0–2.0 m, Tp 6–10 s and Dp1 from E-ESE. The distinction between radar and the buoy directions is related to radar susceptibility to SE trade winds during Spring and Summer seasons. However, the difference did not diverge from prevailing wave regional climate.Copyright

Ocean Eddies’ Influence on Lula Field, Santos Basin, Brazil

Current data measured by an instrumented mooring line deployed at the Santos Basin, in a water depth of 2200 m, show a mean velocity of 0.20 m/s with no preferential direction. Extreme current events detected were associated with the presence of a pair of eddies with a dipole configuration. The jet stream created by the interaction of the cyclone-anticyclone pair was able to generate speeds up to 1.2 m/s at the first hundred meters of the water column. An investigative study with sea surface height anomaly fields processed from environmental satellites clearly shows the eddy structure during extreme current events.Copyright

Separation of Wave Systems in Time Series of Combined Sea States

In some oceanographic applications it is necessary to separate the individual sea state components, or wave systems, that are present in complex wave conditions represented by multipeaked wave energy spectra. Later on, it may be required to realign the original sea states having only the calculated parameters of the splitted spectrum. As an example, this situation may arise when trying to make correlation between time evolution of the sea states with meteorological forcings. To solve this problem a method was developed to follow the time evolution of a given initial sea state using a mathematical tracking procedure. It is based in a “similarity index” between one point of the time series and three previous points. The criterion uses wave parameters Hs (significant wave height), Tp (spectral peak period) and Dir (spectral peak wave direction) to calculate the similarity index. The method selects points that have the highest similarity index as a part of the same type of spectral component, following the time sequence of waves.Copyright