Rev. bras. oceanogr.. 46(1):1-17.1998
Modelling of upwelling in the coastal area of Cabo Frio (Rio de Janeiro - Brazil)
Carlos Carbonel
Laboratorio Nacional de Computação Científica (LNCC/CNPq) (Lauro Müller 455, Botafogo - 22290-160, Rio de Janeiro, RJ, Brazil)
Abslracl: A 1 1Iz reduced-gravity model is proposed to study the hydrodynamic and thermodynamic features of the coastal upwelling area of Cabo Frio (Rio de Janeiro-Brazil). The vertical structure of the model is described by an active layer overlaying a deep inert layer where the pressure gradient is set to zero. For lhe upper layer, the model includes the turbulent version of the momentum, continuity and heat equations. The conservation of heat is represented by a transport equation to describe the thermodynamic changes of the sea surface temperature (SST). The solution domain includes open boundaries in which weakly-reflective conditions are prescribed. Solutions are found numerically on a uniform grid and the fundamental equations are approximated by the finite difference method. Numerical experiments are performed to evaluate the dynamic response of the coastal area of Cabo Frio forced by uniform and non-uniform wind fields. The solutions differ considerably depending on the orientation of the winds. East and northeast winds correlate with colder waters in the zonal coastline of this area and the presence of flows toward Cabo Frio correlates with north wind components. The proposed model is validated with the numerical simulation of an observed event of upwelling, where a time- dependent and non-uniform wind field develops a SST pattern similar as the observations, particularly the extension of the cool water plume in south-west direction and the rapid time variation ofthe SST.
Resumo: Um modelo de gravidade reduzida de I 1Izcamada é proposto para estudar as características hidrodinâmicas e termodinâmicas da área costeira de Cabo Frio (Rio de Janeiro - Brasil). A estrutura vertical do modelo é descrita por uma camada ativa sobre uma camada profunda sem movimento onde o gradiente de pressão é zero. Para a camada superior, o modelo incluí a versão turbulenta das equações de momentum, continuidade e calor. A conservação do calor é representada por uma equação de transporte para descrever os câmbios da temperatura superficial do mar (TSM). O domínio de solução incluí fronteiras abertas onde condições debilmente retletantes são impostas. As soluções são obtidas numericamente numa malha uniforme e as equações são aproximadas usando o método de diferenças finitas. Experimentos numéricos são efetuados para evaluar a resposta dinâmica da área costeira de Cabo Frio gerada por distribuições de ventos uniformes e não uniformes. As soluções diferem bastante dependendo da orientação dos ventos. Ventos E e ventos NE correlacionam com águas fi'ias na linha costeira zonal desta área, e a presença de correntes na direção de Cabo Frio correlacionam com componentes de vento N. O modelo proposto é validado com uma simulação numérica de um evento de ressurgência, onde uma distribuição de vento não uniforme e dependente do tempo gera uma distribuição de TSM similar às observações, particularmente a extensão das águas frias na direção SO e as variações da TSM no tempo.
Descriplors: Coastal upwelling, Numerieal modelling, Cabo Frio.
Descrilores: Ressurgência Costeira, Modelagem numérica, Cabo Frio. 2 Rev. bras. oceanogr.. 46( I). 1998
Introduction at open boundarie$. Many types of open bOllndary conditions have been reported, ali with the purpose Coastal upwelling is an important process of trying to eliminate the artificial retlection of because it brings nutrient rich water to the surtàce, waves at the open bOllndaries(Chapman, 1985). The thereby allowing the development of phytoplankton open boundary conditions, based on the characteristic blooms. Furthermore, the coastal currents and form of the governing equations for shallow water vertical mixing within the diurnal thermocline waves (Verboom, 1982), cOllldbe very effective for provide a way of dispersing pollutants that are sitllations encountered in estllaries (Verboom el. aI.. located close to ports or industrialized cities. Coastal 1983) and for wind-driven ocean problems circulations are often characterized by a meander- (Carbonel, 1982, 1992). like surface flows (Guillen & Calienes. 1981), The purpose of this work, is to investigate associated with the presence of cold sllrt~lce using a I Y2layer model, the wind driven llPwelling temperatures in form of plumes and intrusion of dynamic of the coastal region of Cabo Frio, warm oceanic waters. Coastline geometry, bottom particularly the generation and evolution of topography as well as the driving wind fields, are ali upwelling plumes, which is an observed feature in likely important for determining the transient this region. This paper describes idealized numerical response of coastal areas (Hurlbllrt, 1974; McCreary ca\culations that simulate the coastal ocean's & Kundu, 1988). Major areas of coastal upwelling response to uniform east, uniform north, and non- are located off the Peruvian coast, Oregon coast uniform northeast winds. Next, it goes on to simulate (USA) and northwest Africa. However, coastal the time dependent. respo~e of the model to a wind upwelling also occurs at many other places in the like that observed during an upwelling event along world oceans, including the coastal area of Cabo Frio the Cabo Frio Coast (1971), and compares the in Rio de Janeiro (AlIard 1955; Mascarenhas el. ai., solution with available observations in space and 1971; Ikeda el. ai., 1974). time. There are numerous papers about circulation in coastal areas, some ofthem using analytical methods The observational background of the coastal area (Crepon & Richez, 1982, McCreary el. aI., 1989). of Cabo Frio Numerical models have difficulties simlllating coastal upwelling events, for the reason that some The coastal region of Cabo Frio is located in processes and features such as the upwelling, the Central-Southern Brazilian littoral (Fig. I) and downwelling, coastal jets and mixing are very is characterized by the occurrence of coastal poorly resolved by their grids, because the coastal upwelling events. The bottom topogt!tphy is smooth region of interest is generally part of a much larger and flat, with the contours depth tending to follow complltational domain. Additionally, the delimitation the coastline. The maximllm depth in this coastal of the complltational domain implies that it is area is around 150 meters. The hydrology of the TlL'L'l'''"an to define <;lIitahk hOllTld:IT"\ condi!I<1Tl'
hg. I. loastal ar.:a oll
q = ú) T*/h ,for T> T (4) The model q=O ,for T;'{ T, (5) The model used in this study, has an active layer overlaying a deep inert layer where the in which ú) is a vertical velocity defined equal to pressure gradient is set to zero. We use a Cartesian iJU/Ox, ,and T* is the temperature at the interface coordinate system where Xi represents the planar (the mean value of T and r), that means, q depends coordinates and the usual summation convention directIy to the divergence or convergence of the with repeated indices is used. A schematic view of flows. lhe coastal ocean mode! is presented in Figure 3 . 4 Rev. bras. oceanogr., 46( I), 1998
4Z'
41'
Fig.2. Chartsofsinopticobservations(lkedael aI.. 1974).Inthe upperpaneLSSTfieldwith intormationcollectcdtrom 14:00 hours of08/20/71 to 11:00 hours of 08/21/7 I. ln the lower paneL SST tield with intormation collectcd lrom 23:00 hours of 08/24/71 to 10:30hours of08/25/71. CARBONEL: Modelling of Cabo Frio upwelling 5
...... :.:...... - . . ..:...... J"
. '."< :'. :~:.::':; ;:;:'.: ~y ~':: ;:<;:
Fig. 3. The I Y2 layer modellayout.
Here, the entrainment velocity We only prevents . the interface between the two layers from surfacing (McCreary & Kundu, 1988) and is delined by the smoothing function
,for h < He (6)
(7) and f.*is the Coriolis term in the normal direction. u" ,U" denote the velocity and flux along the axis x". where He is the entrainment thickness and I,. the The weakly reflective conditions in the upper layer entrainment time-scale. are defined by the in-going characteristic of the presented equations. For the coastline, non-slip boundary conditions are prescribed and homogeneous conditions for 11,T are assumed. The weakly reflective condition applied Finite difference solution scheme at the open boundaries, based on the character.istic method, is written in an axis normal to the boundary (x,,), in the following form: The basic equations for the I 1/2 layer model, can be written in a general matrix form as :
ô(UnIch) +c O(UnIch) +G=O (8) oZ oZ OZ Ot oXn -+A-+B-+fC+D\Z+E=O (9) 01 - Oxl - Ox2 ~ _J where, where Z represents the vector variable, E the vector of sources and sink and A, B, C and Q. are the , and FICh c = ~gah G = matrix , described by. 6 Rev. bras. oceanogr., 46( I), 1998
_2;1,1- Z; 11 4(2;/1 ) ,I 2& , '
gh2B/ iP where O , O 4,/ = a z;': 1,/+aZ;~1,/+(1-4a)z;;,~ +az;':'+i +az;'J-1
Uj ] (lI)
is the dissipative interface ; then the finitc difference formulation takes the Lax-Wendroff scheme form O - f O O ç= f O O O , Â m(ZZ:,)+A 4C4~,)+f} 4( Z!:,,)+ÇZ;',+I! 4,71 +E~~,=0 O O O O (12) [ O O O O] where Z represent the mean value vector. The parameter (Xranges in the interval O
opera to r by lateral finite-difference operator 9 B V O O O
Q=OvOO, O O O O [O O O O] where R reprer>entsthe variable and the subscript "B" indicatcs the boundary point, and the decreasing poi!1ts "8-1.8-2" are interior points in an axis normal to the boundary. Afier that, we obtain h at m+ I time leveI, solving equation (8) by the following approximation,
U::1 hmtl li.. * [_ FI!;C, FI ]-[ FI:tchFl] +c Q (T 71/1+clf" )+G.Il-O To establish the numerical mode!, we !y VB uB- /I B- (14) introduce a set of points (XI,X2.t)= (kL1x1, 1L1x2. m,1t) of a discrete grid. The discrete vector variable where U* and h* are the dissipative intertàce for U Z(XIoX2.t)was placed in the same nodes of the grid and h at the boundary points. such that the vector variable is described in the grid as Z;, = Z(kt:.xi,lt:.x2,mM). Results The finite difference approximation is based in centered differences in space and a forward difference in time using a dissipative interlàce. . Here. solutions are evaluated for a coastal ocean forced by uniform and non-uniform wind Considering ~I = ~2 and defining the centered fields. The experiments are focused to the rapid difference operator 8 and the forward differcnce change of dynamic conditions. A coordinate system operator  as: with XI positive eastward and X2positive northward is used. The I IAlayer model of the coastal region of Cabo Frio is forced by wind fields which have a CARBONEL: Modelling of Cabo Frio upwelling 7 spatial structure. Unless specified otherwise, the In Figure 5, is presented the time dependent paral11eter used in the experiments, are the variation of the velocity components and SST off following: The tluid in the layers are initially at Saquarema and Buzios. In the zonal coastline (off rest and the initial value of h =30 m. The densities Saquarema) the cooling of the waters reaches the are assumed p/=1024kg/m3, p' = 1025 kg/m3. The minimum of 15°C in an periqd as short as 2 days Coriolis parameter correspond to the 23°S and the velocity components show a tlow in eastward and taken as I = -5.68 X 10-5 sec-1. The direction (u, < O ) with a small component in Rayleigh friction coefficient is fixed at v=2 x I0-5 southward direction ( uz< O) and when the waters sec-1 . The initial temperatures in the layers are reach the minimum SST of 15°C, the velocity assumed as T = 23°C and T= 15°C and the component in offshore direction increases and the coefficient of thermal expansion is () = 2.6x I0-4 alongshore component decreases (because theterm (OCr'. The time step is ~t=600sec, the ôT/Ox, is suppressed and intluence ofthe term -luz entrainment thickness is fixed in He = 30 m and increases). te = 1f4 day. The coastal ocean is limited to a In the meridional coastline (off Buzios), the rectangle of 1° 30' by 1° using an uniform grid onshore tlow (U1component) forced by the wind spacing of ~x = I/60° ; the number ofdynamic grid during the first stages is suppressed shortly thereafter points are 3902. The computational boundaries are (14 hours) the first signals of cooling of the SST, due partly open and partly closed. the Kelvin wave motion (see SST offBuzios). It was necessary several experiments to chose the mentioned parameters which are the mores adequate to simulate the mean features of the Response to uniform north winds hydrodynamic and thermodynamic transient response of the coastal waters of Cabo Frio (calibrated which Figure 6 shows the model response at day 2 the numerical simulation described in scction and 5 when it is forced by north winds Numerical simulation of a time-dependent upwelling (Lz=0.16N/mz). In the zonal coastline, dose to the event). shore, the upwelling is weak in comparison to the upwelling generated in the east wind case. The presence of cold upwelled water is due the Response to uniform east winds ageosttophic motions only, forced by the nort!~',vindo In the offshore side due the gcn"ti"ol':1icinfiuence a Figure 4 shows the model response at day 2 and zonal current is generateõ:1.)wing in eastward 5 when it is forced by uniform east winds direction. This can explain dlc countercurrent (L,=0.16N/mz). reported in many occasions in this coastal area. At day 2, along the zonal coastline. an In the meridional coastline of this region, upwelling band is generated by the geostrophic upwelling centers are g":;1erated with a stronger motion of waters in the upper layer shoaling lhe h intensity in the downwind side of the capes as tield, increasing the entrainment intluence and observed at day 2. At day 5 the favorable winds help decreasing T. The cooling of the SST is significant, to increase the cold upwelling bando The area of decreasing by almost 7°C in the alongshore bando stronger upwelling is extended up to Cabo Frio. Due the coastline configuration the band is initially In Figure 7 is presented the history of SST and extended up to the Cabo Frio cape. In the meridional the velocity components in the control poinls. The coastline ofthe coastal region there are not signals of SST reaches a minimum only at nay :; oll Buzios. upwelling. Note that the u, component off l3uziús increases a At day 5 the colder water band, generated along little more during the day 5, after the SST reaches the zonal coastline. is wider and turns around the the minimum at day 4. In the control point off Cabo Frio. This is due dynamical consequences of Saquarema, the tlow is going offshore with a the coastal configuration (cape) which generates detlection in eastward direction (u, >0). Kelvin waves in a manner similar to the wind variability as reported by Crepon et aI. (1984). During the experiment, the current system Response to a non-uniform wind field shows a wind dependent response. Along the zonal coastline it is possible to note that close to the shore, This experiment evaluates the solution using a the alongshore velocity component is stronger in possible idealized representation ofthemean features comparison to the offshore side, indicating lhe ofthe observed wind field during an upwclling event presence of a coastal jet. in august of 1971. Rev. bras. oceanogr.. 46( I), 199~
DAY2
S.quareDla _._~- ,.. .,- "..'"",..,..",..-" "...... -...... , " " ",..""".." "..,;, " , .. , , , ,..", ", " ,..., ,, .. 17 , ,...,.." "" ""..., ,..., ,---" ,.....----.... "'*'-"'-"...",-,...,-,.., ",-,...,...", ,,,"- --" ",,.,...... -.....
~~ ;::;: x~ ":';-:.:.::.;"..", ,."",..., , ,..."..,i!!:t."...~
" " " "
Fig. 4. East wind solution. SST and clIrrents at day 2 and 5. The SST contour interval is O.5°e and the velocity arrows are normalized to the maximum 01'23.6 cm/sec at day 2 and 18.3 cm/sec at day5. CARBONEL: Modelling of Cabo Frio upwel1ing 9
24 SSToffSaquarema- SST off Buzios ------....." 22 ...... I- 20 cn ...... ----.-...... cn , 18
16 l O 1, '2. 3 4 5 TIme (days)
0.15 0.1 U1 off Saquarema - U2 offSaquarema ------U1 off Buzios ...... 0.05 U2 off Buzios --
-0.05 -0.1 -0.15 -0.2 -0.25 O 1 2 3 4 5 lime (days)
Fig. 5. Time history 01'SST and velocity components ofl' Saquarema and Buzios (5 km in front) for the east wind solution. 10 Rev. bras. oceanogr., 46(1), 1998
DAY2
DAY5
SaauareUla
16\ ...... -....-......
19\
Fig. 6. North wind solution. SST and currents at day 2 and 5. The SST contour interval is 0.5°e and the velocity arrows are normalized to the maximum of 12.6 cm/sec at day 2 and 10.7 crnlsec at day5. CARBONEL: Modelling of Cabo Frio upwelling 11
24 SSToff Saquarema - SSToff Buzios ------
22
20 \ cn..... cn ", ..... ". 18 ...... "......
16' ..-----...-.------L O 1 2 3 4 5 Time(days)
0.2 U1 off Saquarema - 0.15 U2 off Saquarema ------U1 off Buzios 0.1 U2 off Buzios -- U CI) C/) 0.05 E :...... --...... -.. O '0 ..,....------O -0.05 .\ (i) \ > \ -0.1 "'------.------0.15 -0.2 O 1 2 3 4 5 Time(days)
Fig. 7. Time history 01'SST and velol:ity components olTSaquarema and Buzios (5 km in front) lor the north wind solution. '
Non uniform wind fields are described hy lhe 1'02(t) are time dependent functions. The composition ofpalches ofthe form Figure 8 shows the two-dimensional structures Ip/xI,xz),'fIz(xl'xz)used in the model and the resulting wind field. In this case, '01 (t) and where 'fI1(X"XZ)''fIz(xl,xZ) are the two- l'oz(t) are constant in time and prescribed as dimensional structures of the patches and 1'01(I) , 't01=-0.IIN/m2, 't02=-0.11N/m2. 12 Rev. bras. oceanogr., 46( I), 1998
The Figure 9 illustrates the response of the days to compare with observed spatial SST non-linear model to the non-uniform wind forcing, patterns, presented in Figure 2, and the time showing the velocity and the SST fields at day 2. evolution of the SST in the coastal station of Cabo Afier 2 days a tongue of upwelled cool water is Frio. generated and extended in south-westward directíon Figure 1I íllustrates the response of the non- reaching a minimum in &ont of Saquarema. In this linear model to the time dependent and non-uniform sector the SST reaches the minimum of 15°C. wind forcing, showing the velocity and the SST Warmest temperatures occur well offshore and tields at 2 and 3 days. Afier 2 days a tongue of eastward approaching its initial value. The velocity upwelled cool water is generated and extends in field shows a current going offshore, which is south-westward direction reaching a minimllm forming at the coast and by continuity has !low temperature of 16.3°C in &ont of Saquarema. Note contribution along the coast &om the east side that a cool water cell enclosed bya contour of 17°C is as a coastal current and &om the west side as a formed offshore. This cell is mainly a consequence of coastal countercurrent. The maximum velocity the changes in direction and magnitude of the wind obtained in the flow field is 17.7 cm/sec. The foreing. Remember that in the previous test calculated SST pattern is similar to the observed one calculation , using the same spatial structure of (upper panel of Fig. 2) characterized by the the wind but constant in time, the cool water cell upwelling center in &ont of Saquarema and a offshore is not present in the solution a!ter 2 days spreading of cool waters of arollnd 17.5°C in south- (Fig. 9). westward direction. . Afier 3 days the tongue of cool water is more intense, due the persistence of favorable wind. It reaches an absolute minimum of 15°C in a band Numerical simulation of a time-dependcnt between Saquarema and Cabo Frio which extends upwelling event offshore in south-west direction. Warmest temperatures occur well offshore and eastward approaehing its initial value, and SST rises to 23°C. In this numerical simulation, the model 01'the The velocity field shows a current flowing offshore, coastal region of Cabo Frio is forced by a wind lie1d which is being formed at the coast and by continuity which has a spatial structure and a time variability. has flow contribution along the coast, from the east The wind fieIds are composed of patches of the lorm side as a coastal eurrent and &om the west side described in (15). The horizontal structure of the as a coastal counterflow. In the offshore side, wind stress components are proposed taking into there is a drifi in eastward direction which is not accollnt observed pattern. The structures really a surface countercurrent, it is only a 'f/t(X"X2), 'f/2(X"X2) used in the modeI are the deflection of the flow due the response of lhe coastal same showed in Figure 8. The hourly observations water to the non-uniform wind tield forcing used in (Fig. 10) at an industrial meteorological statíon this simulation, with a tendency to form a cyclonic ("Companhia Nacional de Alcalis", situated on the gyre. The maximum velocity at third day is 26.5 coast a little west of Cabo Frio) were corrected in cm/sec. order to extrapolate for the ocean, increasing the Figure 12 shows the calculated time dependent wind velocities in a 30%. The time variation of the variations of the SST in points representing wind stress functions 'o I(t) and '02 (t) were Saquarema (at the shore) and the coaslal station of calculated using the aerodynamic square law. In this Cabo Frio. The time-dependent patterns in these simulation, for calibration purposes, were chosen points are particularly similar to the obscrved in the vallles for the wind drag coefficient cw=2.25xI0-3 coastal station of Cabo Frio. The SST dropping is and the Rayleigh friction coefficient v=1.8 x I0-5 very intensive during the second day due higher wind sec-I. velocities. A wind relaxation during the third day The observed wind velocities at the beginning increases the SST during some hours. The resuIts indicate that the model describes 01' the upwelling event were very weak (2m/sec) and upwelling conditions were not reportcd. remarkably well the time-dependent physical Additionally, information about the wind pattern and features of the observed coastal upwelling and the dircction bcfore the initial date was not enoug,h to rapid change of SST in the coastal regionof Cabo define a correet initial state, therefore, the initial Frio. The modeling results give support to the conditions were defined at rest, which are aeeeplable hypothesis that the spatial pattern of the tongue of to represent ocean condition under weak winds. The upwelling in this region is mainly drivcn by the simulation of the upwelling is started at O hours of spatial configuration of wind field in this coastal 08/18/71 and integrated forward in time during 3 region. 'Ulnll'!xmu ;)lP <11P:YZ!llHU.IOU;).1\1SA\OJ.1\1'\~!;)0I;)A ;)ljl pun "0 S! S;).lnpIlJ~S ;)ljIJO InAJ;)~U! JIl\)~U{););'IlU. 'PI;)!! PU!A\ ;'i'LI!IIIlS;"\Jpun (LX' IX) Ltil . ( LX . 1.r) 'til S;"\JIlI:1IlJIS 111l10!SU:1lU!P-O\\L 'S 'TIU
~ ------. _o..0_..0_- _...._...... _..______...__...______....._..___...... ___...______...... ______.._.. ::::::::::::::: :~::::::::::::::::::::::::::::::::::::::::::::::::: -: ...... --..----...... -- 14 Rcv. hras. oceanogr., 46( 1), 1998
Fig. 9. Solution by non-unit{)rmwind th:ld. The arrows are normalized to the maximum velocity 01' 17.7 cm/sec and the contour intcrval 01' the SST is 0.5°e.
5 zonal campo meridional campo
o n...... _...... _...... ___...... , "......
ô CI) fi) g -5 i ., '0 I I. ~, O Ir, r-~:\ :\ Ar, ã) . ,/ I' \..., Ií \j \. .,'i '.,i\/ \. I: \" ,--~ > \1 \ f,i \__J 'I \-../-\ '---'l -10
-15 o 10 20 30 40 50 60 70 80 Time (hours)
Fig. 10. Local timc variations 01'thc wind \'l.'locity (in components) collccted in a l11eteorologicalstatioll a littlc \Vcst 01' Caho Frio. CARBONEL: Modelling 01' Cabo Frio upwelling 15
AT 48 HOURS
AT 72 HOURS
Saquarema
......
Fig. 11..Simulation n.:sults 01'thl.: Cabo Frio I1H>dd.The arro\Vs are normalized to the maxil11um vclocity and the I.:Ontour interval 01' the SST is 0.5°(:. I\t48 hours alieI' the wind is blowing the upwelling eenter is located in Ihmt 01' Saquarema delimited by the SST contour 01' 16. 5°C. the maximum velocity is 19.9 I.:m/5I.:c.1\t 72 hour5. lhe minil11Ulll ~~T I.:ontour 01' 15.5°C ddimitl.:d a band 01' cold water extl.:nded oll"horl.: in south-west direetion and the lI1aximul11vdocity is 26.5 em/see. 16 Rcy. hras. occanogr.. 46( I). 1998
25 SST Cabo Frio(Observed) 24 SST Saquarema(Calculated) SST Cabo Frio(Calculated)
23 1--...... 22
21
20 cn 19
18
17
16
15 O 1 2 3 Time (days)
Fig. 12. limc history 01' thc COl1lputcJ 5Sl in thc coastal points 01' Saquarcma anJ Caho Frio anJ the ohscrvcd SST in thc coas tal station ol'Cabo Frio.
Conclusions idealized spatial structure. The results describe the rapid evolution, during 3 days, 01'a plume 01' cool A modcl for the coastal area 01' Cabo Frio upwelled water extended in southwest direction, and (Rio de Janeiro - Brazil), based on the non-lincar the time response of the SST in the Cabo Frio I Yzlayer model, is presented. The model includes station. These results compare remarkably well with the hydrodynamic momentum and continuity the observations in space and time. The calculated equations; a thermodynamic equation to describc the current system is characterized by a current flowing changes of SST, and a properly treatment 01'the otlshore, which is 1'ormedat the coast, and by signals open boundaries. The equation system is of eastward tlows otlshore. During the simulation, approximated by the tinite ditlerence method. due the changes 01'magnitude and wind direction, It was analyzed the dynamic response 01'the cells of cool upwelled water separate frol11the initial coastal region of Cabo Frio. East winds generatcs an upwelling center flowing in southwest direction. The upwelling band along the zonal coastline 01' the 1110dellingresult gives support to the hypothesis that region. North winds prodllces a weak ageostrophic the observed tongue of upwelling is mainly driven lIpwelling at the zonal coastline but offshore a by the spatial contiguration 01' wind tield in this castward tlow is obtained. In this case, along the coastal region. meridional coastline 01'the region, the upwelling is Conclusively , the success1'ullyobtained results more intense. When the model is forced by a l1on- in the numerical experil11entsvalidate the conceptual 1IIliformwind tield, representing an idealized \\'ind formulation of the model presented in this papel'. p;lttern of the region, it was possible to reprodllL'ca Improvements of the model for further application is plume of cool upwelled water \vhich intensifiL's in possible increasing the complexity with processes sOllthwest direction. In this experiment it was which were not consider in this papel'. vcritied the presence 01' coastal eastward tlows. The presence 01' eastward tlows in the solutions, associatcd with north wind components, might Acknowlcdgements L':o;plainthe prcscnce 01'"countercllrrcnts" reportcd in many occasion in this coastal area. The author was supported by CNPq grant no. A time-dependent simulation of an upwclling 381575/97-7. Thanks to the reviewers, their event in 1971 is obtained successflllly. The modcl is cOl11mentswere helpful in improving the manuscript. !i,rced by a time dependent wind tield with an CARBONEL: Modclling 01' Cabo Frio upwclling 17
Rcfcrcnces Mascarenhas Jr., A. S.; Miranda, L. B. & Rock, N. 1 1971. A study of oceanographic conditions in the Allard, P. 1955. Anomalies dans les températures de region of Cabo Frio. In: Costlow .Ir.. J. D. ed. I'eaux de mer observées au Cabo Frio (Brésil). Ferilitty ofthe sea. New York, GordOll& Breach BulI. Inf Com. cent. Oceanogr. Études Côtes, 2: Science Publishers. p. 285-308. 58-63. McCreary, 1 P. & Kundu, P. 1988. A numerical Carbonel, C. 1982. Numerisches model der investigation of the Somali Current during the zirkulation in auftriebsgebieten mit anwendung SOllthwestMonsoon. 1 mar., Res., 46( 1):25-58. auf die Nord-Peruanische Kueste. Ph.D. Thesis. 1nstitute fuer Stroemungsmechanik, Hannover McCreary, J. P.; Lee, H. S. & Entield, D. B. 1989. Universitaet. 92p. The response of the coastal ocean to strong offshore winds: with application to circulations Carbonel, C. 1992. Numerical modeling of layered in the Gulfs of Tehuantepec and Papagayo. 1 ocean fluids on a limited-area domain. RelatÓrio mar. Res.,47(1):81-109. 33. Instituto Politécnico do Rio de Janeiro. 35p. Stech, L. & Lorenzzetti,.I. 1992.The response of the Crepon, M. & Richez, C. 1982. Transient upwelling South Brazil Bight to the passage of wintertime generated by two-dimensional atmospheric cold fronts. 1 geophys. Res., 97(C6):9507- 9520. forcing and variability in the coastline. 1 phys. Oceanogr.,12(12):1437-1457. Torres A. & Santana, A. I. 1994. Resposta local da Crepon, M.; Richez, C. & Chartier, M. 1984. Effects ressurgência costeira de Cabo Frio a passagem of coastline geometry on upwelling. .I. phys. de um sistema frontal. Pesquisa Naval, 7:107- 116. Oceanogr., 14(8):1365-1382.
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