327 HARARI.cdr

Journal of Coastal Research
1560- 1563
SI 39
ICS 2004 (Proceedings)
Brazil
ISSN 0749-0208
Numerical Modeling of the Hydrodynamics in the Coastal Area of
Sao Paulo State Brazil
J. Harari†; R. Camargo‡; C.A. S. França†; A. R. Mesquita† and S. S. Picarelli†
†Dept. of Physical, Chemical and Geological
Oceanography,
Institute of Oceanography,
University of Sao Paulo, Sao Paulo, SP, Brazil,
[email protected] ; [email protected] ;
[email protected] ; [email protected]
‡ Dept. of Atmospheric Sciences,
Inst. of Astronomy, Geophysics and
Atmospheric Sciences, University of Sao
Paulo, Sao Paulo, SP, Brazil,
[email protected]
ABSTRACT
HARARI, J.; CAMARGO, R.; FRANÇA, C. A. S.; MESQUITA, A. R. and PICARELLI, S. S., 2006. Numerical
modeling of the hydrodynamics in the coastal area of Sao Paulo State - Brazil. Journal of Coastal Research, SI 39
(Proccendigs of the 8th International Coastal Symposium), 1560 - 1563. Itajaí, SC, Brazil, ISSN 0749-0208.
A numerical model was implemented for the whole coastal area of Sao Paulo State, Brazil, based on the Princeton
Ocean Model. The model grid has 150 x 450 points and 11 sigma levels, with uniform resolution of 1 Km in the
horizontal, and time steps of 180 and 6 seconds for the internal and external modes. The main advantage of the
implemented model configuration is the possibility of using nested grids in estuarine regions of interest and
subsequent use of dispersion and sediment transport models. Numerical experiments consider the coastal circulation
driven by tidal, meteorological, density and river effects, separately or combined. A simulation with all the forcing
effects shows the importance of the coastal channels in the amplification of the circulation, particularly in the
Cananeia Iguape estuary, where surface currents reached 84.6 cm/s. In general, river effects are not very significant
in Sao Paulo State coastal areas but, in the central part of the shelf, the low salinity induced by the rivers flows
produces surface currents towards the open sea and strong deep currents towards the continent. The results of the
model runs may be used in several applications, such as navigation operation and security, sediments transport
estimates, monitoring of beaches evolutions and water quality control, especially in nested grids covering the
estuaries and internal shallow regions.
ADDITIONAL INDEX WORDS: Three dimensional currents; tidal and general circulation.
INTRODUCTION
Numerical models have been used more and more in studies
of oceanographic processes, giving basic information of the
hydrodynamics and the properties distributions in areas of
interest. Nowadays, these models may be used with linear or
curvilinear grids, constant or variable grid spacing, several axes
orientations (EW - NS, parallel - perpendicular to the coastline),
etc. Usually, the model and grid configurations are defined
aiming to optimize the use of computacional resources, for
instance by minimizing the number of grid points in land and
maximizing the number of oceanic points in sub-areas of
interest. Additionally, the access to modern computational
resources allows the processing of extremely refined grids, with
large number of mesh points, small spacing and, consequently,
very small time step.
These characteristics of the modern modeling techniques
make possible their intensive use in many fieds, practical /
applicative as much as scientific / academic (HARARI and
CAMARGO, 2003). Most of the practical applications are in
studies of the dispersion of substances and / or properties, such
as tracers, nutrients and oils (AHSAN et al., 1994; BANG and LIE,
1999) and in the evaluation of the transport and deposition of
sediments (WANG, 2001; WANG and PINARDI, 2002).
On the other hand, the use of hydrodynamical numerical
models in coastal applications depends on the quality of the
currents simulations, which in turn depend on the horizontal
spacing. In the coastal area of Sao Paulo State, Brazil, that has
been reached through the progressive decrease of the grid size
from 10 Km (HARARI and CAMARGO, 1994; CAMARGO and
HARARI, 1994) to 1 Km (HARARI and CAMARGO, 1998) to
below 100 m (HARARI, CAMARGO and CACCIARI, 2000;
HARARI, CAMARGO and MIRANDA, 2002).
The latest researches on the circulation in the coastal region
of Sao Paulo State deal with the implementation of models
considering three subregions of the shelf: the northern, central
and southern parts (HARARI, TONIN and CAMARGO, 2002;
HARARI, CAMARGO and MIRANDA, 2002; HARARI, PICARELLI
and CAMARGO, 2002). Special interest has been considered in
the tidal circulation of the central part area, named Baixada
Santista (HARARI and CAMARGO, 2003a).
This publication shows the implementation of a model with a
single grid that covers the whole internal shelf of Sao Paulo
State, with an horizontal resolution of 1 Km. The present
version of the model allows simulations of the circulation due to
tidal, meteorological, density and river effects, combined in
several forms, in order to evaluate their relative importance.
The main advantage of the implemented model configuration
is the possibility of using nested grids in estuarine regions of
interest and subsequent use of dispersion and sediment
transport models. Another advantage is concerned with
studying the propagation of dynamic systems along the shelf
through coastal waves, such as the ones generated by cold
fronts.
METHODS
The numerical modeling is based on a version of the
Princeton Ocean Model (POM) adapted by HARARI and
CAMARGO. The POM was developed by BLUMBERG and
MELLOR (1987) and is presented in details by MELLOR (1998);
the main characteristics of the model are: the complete three
dimensional non linear equations are written in flux form, with
Boussinesq and hydrostatic approximations, and the diagnostic
equation of state; bottom friction is represented by the quadratic
law; the vertical solution is based on a sigma coordinate, which
follows the bottom relief; a second order turbulent closure
scheme is used to compute the coefficients of vertical viscosity
and diffusion, with equations for the turbulent kinetic energy
and the length scale of turbulence; the horizontal viscosity and
diffusion have Smagorinsky parametrization; the time
evolution adopts the splitting into external and internal modes,
with different time steps; concerning the numerical integration
of the model, a C grid is employed and the leapfrog scheme is
used for the time and horizontal domains, while an implicit
scheme is used in the vertical. Examples of recent applications
of POM in studies of coastal circulation are found in PULLEN
and ALLEN (2000, 2001). Among the alternatives of the POM
processing, there are the 2D e 3D versions, the last one having
the options of temperature and salinity fields constants or
Journal of Coastal Research, Special Issue 39, 2006
Numerical Modeling of the Hydrodynamics in the Coastal Area
1561
Figure 1 Model computation of surface currents at 02:00 GMT of 20 January 1997 in the whole coastal region of Sao Paulo State (vectors
th
every 5 line and column of the grid).
variable in time. The basic version of this model is of public
domain and may be found in
http://www.aos.princeton.edu/WWWPUBLIC/htdocs.pom/.
The adaptations of Harari and Camargo concerned basically
on making flexible the code for independent processing of the
ocean circulation contributors: tides, winds (local and remote),
density and rivers. Obviously, the correspondent circulations
may be combined in several ways (considering, for example,
only tides and winds, and excluding density and river effects).
Other important adaptations were relative to the introduction of
several options in the boundary conditions: the exact
specification of tides and mean sea level, radiational conditions,
no gradients conditions and relaxation schemes.
The grid that covers the internal continental shelf of Sao
Paulo State is rotated 62° (clockwise) relative to the EW
direction, being formed by 150 x 450 points with constant
horizontal spacing of 1 Km and 11 vertical levels, placed on
sigma values of 0.0 (surface), -0.03125, -0.0625, -0.125, -0.25, 0.5, -0.75, -0.875, -0.9375, -0.96875 and -1.0 (bottom); the time
steps of the simulations are 180 and 6 s. This grid has 54742
oceanic points and 12758 points in land, with maximum depth
of 158.82 m. Other important parameters adopted in the model
processing are: constant in Smagorinsky horizontal diffusivity
= 0.01; bottom roughness parameter = 0.002 m; ratio of
horizontal heat diffusivity to kinematic viscosity = 1.0;
advective terms of external mode updated at every 5 external
time steps; and finally, three points temporal and spatial
smoothers were applied to prevent solution splitting and control
numerical noise.
The model run for the period of December 1996 to February
1997, considering thus mean summer conditions of temperature
and salinity, extracted from LEVITUS and BOYER (1994); typical
river discharges (for the summer season) are given by FCTH
(1997); the tidal elevations at the boundaries are based on
results of the global tidal model of LE PROVOST et al. (1994) and
pelagic tidal measurements in the shelf (MESQUITA and
HARARI, 2003); mean sea level oscillations are given by coastal
tidal stations; finally, the winds at the surface are extracted from
the global atmospheric model of NCEP / NCAR, available at
http://www.cdc.noaa.gov/cdc/data.ncep.reanalysis.html.
RESULTS
An example of the model outputs is shown on Figure 1, with
surface currents at 02:00 GMT of 20 January 1997, when a
storm surge during spring tides induced a huge increase of the
mean sea level in the coast. This figure shows horizontal vectors
th
every 5 line and column of the grid, while Figure 2 represents
all the current vectors computed in three subareas with
important coastal systems: the estuarine area of CananeiaIguape (Figure 2a), the estuarine region of Santos-Sao VicenteBertioga (Figures 2b and d) and the Channel of Sao Sebastiao
(Figure 2c). Figures 2a, b and c are relative to surface currents,
while Figure 2d represents the depth-mean currents. Note that
these results consider all the circulation forcings in the basic
grid of the model, but no nesting in any coastal region.
Maximum computed surface currents (at the time above
cited) were: 88.8 cm/s due to tides only (at the grid point of
column, line = 27, 46 see Figure 1 for location); 97.1 cm/s
generated by tides and winds (again at the point 27, 46); 129.3
cm/s due to tides, winds and density (at the point 33, 35);
finally, 84.6 cm/s due to tides, winds, density and river
influence (at the point 27, 46).
The Figures stress the importance of the coastal channels in
the amplification of the circulation, due to continuity effects,
particularly in the Cananeia-Iguape estuary, where the
maximum values above cited were computed.
In general, river effects are not very significant in Sao Paulo
State coastal areas but, in the central part of the shelf, the low
salinity induced by the rivers flows produces surface currents
towards the open sea and strong deep currents towards the
continent (see the surface currents on Figure 2b and the depthmean currents on Figure 2d).
Journal of Coastal Research, Special Issue 39, 2006
1562
Harari et al.
Figure 2. Currents computed by the model at 02:00 GMT of 20 January 1997: at the surface, in the estuarine area of Cananeia - Iguape (a);
surface and depth-mean currents in the estuarine region of Santos - Sao Vicente - Bertioga (b and d); at the surface, in the region of the
Channel of Sao Sebastiao (c); all the computed vectors are represented.
ANALYSIS
The next step on the researches is concerned with the use of
the implemented modeling to subsidize several applications in
the oceanographic sciences, particularly in aspects where the
current systems are important. The main applications are as
follows:
Navigation operations and security, by informing boats about
the sea surface currents and elevations.
Support to bathymetry surveys (FREITAS, 2004), giving the
surface elevation in the exact position and time of the depth
measurement, whose subtraction removes instantaneous sea
level variations (effects of tides and winds, for example).
Maps of biochemical properties distributions (nutrients,
silicate, etc), as measured by BARRERA-ALBA et al. (2002,
2003) in the estuary of Cananeia-Iguape, are analyzed as a
function of the coastal currents computed by the model.
Measurements of sedimentation and observations of beaches
evolutions are compared with residual currents computations
for long periods of time (order of months) or extreme
meteorological events, as done by ROCHA (2003).
Dispersion models are coupled to the hydrodynamical ones,
in order to estimate the distribution of properties and the
evolution of particles positions (HARARI and GORDON, 2001;
HARARI, GORDON and CAMARGO, 2002). This is especially
important for oil spills and the operation of submarine
emissaries of effluents, contributing to water quality control.
Storm surges in the coast are reproduced through the model,
by specifying the correspondent boundary conditions:
oscillations of the mean sea level (by filtering measurements of
coastal tidal stations), surface wind data (generated by global meteorological models) and estimates of the fields of
temperature, salinity and river discharges (based on typical
standards). After reproducing the observed sea surface levels,
the models are re-processed considering combinations of the
forcing effects, in order to evaluate their relative importance
(CAMARGO and HARARI, 1994).
Altimetric measurements of the missions Topex / Poseidon
and Jason1 (AVISO, 1996, 2001), correspondent to variabilities
of the sea surface level, are processed (FRANÇ A, 2000; FRANÇ A
et al., 2001) and subsequently used as boundary conditions of
hydrodynamical numerical models and validations of the
models results; that allows the determination of standards of sea
surface variabilities (considering seasonal, annual and interannual time scales).
CONCLUSIONS
The applications of the numerical modeling will allow an
increase of the knowledge about the oceanographic processes in
the coastal region of Sao Paulo and, also, improvements of the
implemented circulation models themselves.
Among the processes planned to be studied, there are: the
effects of cold fronts intrusions in the coastal circulation; the
interactions between the circulations generated by
meteorological and tidal effects (with emphasis on their threedimensional structure); and the interactions between the coastal
circulation and river discharges.
About the modeling, there are several improvements to test,
the main ones being: better specification of river effects (with
formulations that consider both currents and low salinities that
penetrate the estuaries); splitting of local and remote wind
effects; comparison of the responses of sub-areas of interest
covered by grids of different resolutions (in which the same
forcings were specified); best choices of boundary conditions
formulations; and increase of horizontal and vertical
resolutions.
ACKNOWLEDGMENTS
To Institute of Oceanography and Institute of Astronomy,
Geophysics and Atmospheric Sciences, of the University of Sao
Paulo, for providing all the necessary means to accomplish this
research.
Journal of Coastal Research, Special Issue 39, 2006
Numerical Modeling of the Hydrodynamics in the Coastal Area
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Journal of Coastal Research, Special Issue 39, 2006