T?p chi Khoa hoc va Cong ngh? BiSn; Tap 14, S6 1; 2014: 10-17 ISSN: 1859-3097 http://www.vjs.ac.vil/index.php/jmst
M O PHONG HE DONG CHAY VUNG BIEN N A M BO - VINH THAI LAN
Pham Xuan Duong
Vien Hai duang hoc-Vi?n Han lam Khoa hpc va Cong nghe Viet Nam E-mail; [email protected]
Ngay nhan bai: 15-8-2013
TOM TAT: Bai bdo trinh bay mQtsd Icdt qua nghien cmi chi ^p dong chay cr vimg biin Nam Bo - vinh Thai Lan vao miia gio Bong Bic (mim kho) va miia gio Toy Nam (miia mua) bdng mo hinh ROMS. Cdc thong si khi tirrmg, thiy triin biic xa, bic hai clwjc liy tit bo si li^u biin loan ciu co do phan giai '/, df. Cdc kit qua nghien cm cho thiy, vao miia gio Bong Bic, viing biin Nam Bo xudt hien dong chdy dgc bi (hucmg Bong Bdc xudng Tdy Nam) co tin sudt cao chay vdo vinh Thii Lan. Do ddc diem nay md truong ddng chdy trong vinh Thdi Lan tgi nhiiu thii diim hinh thanh hodn luu khep kin a vimg tit vi do f tra len Vdo miia gio Tdy Nam, hien tuang nay cUng xudt him nhung vdi Idn xudt thdp vdi hucmg ngucrc lai
Tit thda: He dong chdy, miia gio Bdng Bdc, miia gio Tdy Nam, hoan luu khep kin.
MO DAU
Vimg biSn nghien cmi keo dai til Binh Thuan (Viet Nam) dSn cue Nam Thai Lan (hinh 1) la khu vuc co dia hinh day biin kha phiic tap, chia cat manh, mat do chia c4t day va dp sSu bien biSn ddi tit vai met din hang tram metj hinh dang duong bo bien phiic tap vai rat nhieu_dao Ion nho nSm rai rac a ca phan trung tSm lln gin bo. DJc diem nay anh huong tdi che dp hoan luu nuoc noi chung va che dp dao dpng m^c nuac, thiiy triSu noi rieng [2].
Vi?c nghien euu trutmg dong chay trong vvin^ bien viing biin Nam Bp - vinh Thai Lan CO tam quan trpng to lan d6n viec nghiSn euu mOt so jTnh vjic khac nhu nuac trai, nghe ca, lan truyen chat 6 nhilm, xam nhap man, thoat lu ra vinh Thai Lan ... Su tuang tac dpng l\rc va moi truong giiia Bien Dong va he thong song Ciiu Long ciing dong vao su hinh thanh che dp thuy luc a khu vuc nay.
Trong nhiing nam truoc day, mot sa tac gia trong nuoc cung da tinh toan dong chay a khu
vuc nay va tren toan Biin Dang theo mo hinh 3D va da xay dtrng clu tnie dong chay va su bien thien trutmg nhiet - muoi theo miia [1].
>lhung cac nghien ciiu nay vln chua noi ve sit ton tai va dac dilm cu the ciia hoan luu a khil vuc nay nhu thi nao, dac biet it quan tam t « su bien doi giong va khac theo miia va cac thang tin ve hoan luu o cac ting sau vln con gay nhieu tranh cai.
Hien nay ROMS khang chi co mpt phien ban duy nhSt, no dupe phat triln trong theo chl do ma cua cac t8 chiic vai mpt lojt cac phien ban khac nhau. Thong tin tren ROMS la co sin tai trang web chinh thiic cho cac nha phat triln hay ngutri diing ROMS 141! (http://marine.rut- gers.edu/po/index.php?model=roms&page).
Mo hinh ROMS sii dung h? tpa dp Sigma c6 uu diem la mo phong anh huong ciia dia hinh toi dong chay trung Ihifc han cac mo hmh sai phan thang thuong. Nhupc dilm ciia no la xuat hipn sai so sa hpc trong qua trinh tinh gradient ap suat t?i cac vj tri co dp die lan ma khong the \oai bo dugc hoan toan. Nha phuang
Mo phong he dong chay viing bien Nam Bg ...
phap tai tao parabolic do Shchepetkln va McWiliams de xuat [8, 9], dugc sti dung trong ROMS da cho phep giam sai s6 tai mue co thg chap nh^n dugc.
PHlTONG PHAP NGHIEN CUtJ H$ phuong trinh eo ban cua ROMS viet tiong tga dg De Cac (x, y, z, t) co dang co ban tir (1) den (7):
Phuong trinh lign tyc
Cae phuong trinh dgng lugng Reynolds:
| + v . V « ^ - « - | - y v = - ^ - ^ F „ - ^ Z ) „ (2)
% + vy/v.,w^ + fu = - ^ + F^ + I\ (3)
^ + vWT = Fr-i-Dr
f + v.VS = F5 + B 5
Trong do: u, v, w cac thanh phan van toe theo tryc x, y, z tiong hg toa do De Cac; / : tham so Coriolis; T: nhigt dg, S: dg muoi,
dx PQBX dy p^dy ^ 8z\ M dzj Dv = ^ ( j ^ j u f e ) '^ ^^^ ^ ^ " ^ P*^^" ^°^ ^^
khuech tan roi theo phuang thang dting.
H? phuang trinh ca ban eua ROMS vigt tiong tga dg Sigma, tga dO cong tr\rc giao va cac ki higu tham khao trong tai li?u tieng Viet [l]v^ tieng Anh.
ROMS sir d\ing ludi cong tr^rc giao [7], do vay mien tinh co the la mien eong bat ky va hg
tog do tuong thich voi dia hinh theo phuong thing dung la hg tga dg Sigma (O" hoac s, xem tiong [4]). Viing nghien ctiu la viing bien Nam B6 (Viet Nam) va toan bo vinh Thai Lan (hinh I).
Phuong trinh dgng lugng theo phuang
thang dung: ^ = - ^ (4) Phuang truih trgng thai p = p{S,T,P)va
gia thigt tiiiiy tTnh: % = Pg (5) Cae phuang trinh khuyech tan nhiet muoi:
(7)
Hmh 1. So do vi tn vung nghien ctm Duong ba dugc lay tu so ligu duong bo eiia NOAA eo tign tiang web http://www.ngde.noaa.gov/eoast/getcoast.html
Dia hinh vung nghign ctiu dugc lay tii s6 ligu phan tich ET0P02 (NGDC, 1988) va co higu ehinh them vol cae s6 lieu do dg sau th\ie te ti viing nghien ctiu.
Viing nghien euu dugc phii kin boi mgt mgng luoi 90 x 100 digm (hinh 2) theo phuong nam ngang va 5 lop sigma theo phuang thang dung vol zJxa8-24,5A7n, Ay'=2-\6km, ,4z»1^400m va buoc thoi gian At = 3^5 la phu hgp vcfi mo hinh.
Thong lugrig, nhiet, bay hoi, mua, gio, stic cang be mat bien theo miia dugc lay tu COAD [5]. Gio ven bien la rat khac nhau, rat kho dg do luong tir xa, str dung so ligu gio thong qua mo hinh khi quyen (COAMPS) va tu truygn hinh V? tinh seatterometers (puikSCAT) [3].
Cae dieu kien bien ma phfa Bac, phia Dong va phia Nam mo la s\r kSt hgp giiia cac thanh phan binh liru phan xa ben ngoai [6], cac dieu kign nay dugc tinh bang each sit d\ing cae dii ligu khi tugng.
Phgm Xuan Duong
Hinh 2. M^ng ludi cho viing tfnh Doi vol thiiy trieu chung toi sti dyng dii ligu tit TOPEX / Poseidon toan cku phien ban 7.1
(TPX07.1), no la mgt mo hinh thiiy trigu dgi duong toan cau, phu hgp tot nhat khi thuc hien tiong mgt mien hinh vuong.
Bien long huong song dugc xac djnh qua luu lugng va mat cat udt eiia cdc ciia song iVIg Kong va song Chao Phraya (Thai Lan). Trong m6 hinh chiing toi sti dung liru lugng nutic trung binh thang cua mgt s6 tram thuy van tign song Me Kong (http://www.mrcmekong.org, www.tiengiang.gov.vn) va song Chao Phraya (lay tir http://webworld.unesco.org/water/ihp/- db/shiklomanov/part%274/ASLi/Thailand/2TH
%60Chap%20Phraya%20at%20NakhonSawan .htm). S6 ligu ve Itru lugng binh quan thang tgi cac tiam thuy van nhu trong bang 1.
Bang 1. Bang liru lugng (mVs) tiung binh thang eua song Me Kong va song Chao Phraya.
Trim Thing
SOng Ti^n SOng H^u
OSu Tidng ViimCfi Dfing vsmca TSy Chao Phraya
3 700 2 650 11,400
3 050 16 400 4300
21.aOD 5 210
5 800 1,470
KtT QUA NGHIEN CUtl
Nghien euu hoan liru dong chay trong viing bien Nam Bg - vjnh Thai Lan bang mo hinh ROMS, mo phong truong dong chay trong thdi gian dai theo miia, miia mua (miia gio Tay Nam) va mua kho (miia gio Dong Bae), dii ligu dugc xuat ra lign tue eho tung gid (tu 0 gid ngay 1/1/2009 - 31/12/2010). Cac ket cjua tinh toan duge the hign qua ban do phan bd trudng vector ddng chay eho phep nhan dinh eae k ^ qua tinh toan cd cac dgc diem nhu sau:
Anh hvovg cua ngo^i lire len truoTng ddng chay
Tgi tang mgt: tiirdng ddng chay the hi?n rd dugc cac viing bi anh hudng mgnh bdi cac liic tac dyng. Nhu viing ehiu anh hudng mgnh ciia nudc sdng Me Kong dd ra (viing gan cira song), viing nudc ehiu s\r chl phdi manh me bdi
trudng gid (ngoai khai Biin Ddng), viing chiu tac ddng mgnh me bdi su Ign xudng ciia thuy tiigu nhu d ctia, trong vinh Thai Lan va viing bj anh hudng ciia dudng bd tdi hoan luu dong ehay tai day (hinh 3-5).
Hinh 3. Phan bo trudng ddng chay tang mat vao mgt thdi diem cua thang 1/2009
M6 phong hg dong ehay viing bien Nam Bo ...
Hinh 4. Phan bd dg muoi va trudng gid (trai) va phan bd bign do sdng thanh phan M2 (phai) vao thang 7/2009
thg khac nhau. CJ vjnh Thai Lan, tai nhieu thdi diem trudng vector dong chay cd xu the chung tai cae lap, trudng ddng ed hudng tir ngoai khoi vao bd, tuy nhien trudng ddng chay giiia Idp tien va Idp dudi cd su lech nhau vg hudng. Net ndi bat eua trudng ddng ehay d vung bien Nam Bg (Birih Thuan - Ca Mau) la xudt hien ddng ehay Bac - Nam manh vao mua khd va ddn^
chay ngugc lai nhung yeu hon va thdi gian xuat hign it hon vao miia mua.
Hinh 5. Phan bo trudng ddng chay tSng m^t vao mgt thdi diem cua thang 7-2009
Hinh 6. Phan bd trudng ddng chay tang giiia vao mgt thdi di^m cua thang 1/2009 d tang giiia (hmh 6, 7) va t^ng day (hinh 8, 9), phan bo tnrdng ddng chay cho thdy hoan luu d cac tang chiu tac dgng ciia cac luc ngoai it hon nhat la tang day tac ddng cua tiTidng gid td ra md nhgt chi cdn chju anh hudng mgnh cua nudc sdng, thiiy trieu va ma sat day. Dgc diem chung cua hinh thai ddng chay d tat ca cac Idp la trudng ddng chay phSn ra thanh cac khu v\re cd hudng va toe dg khac. T i ^ iihien hudng d cac vung khac nhau trong mdi tang deu cd xu
Hinh 7. Phan bo trudng ddng chay tSng gifla vao mgt thdi diem ciia thang 7/2009
Hinh 8. Phan bo trudng ddng chay tSng day vao mgt thdi digm cua thang 1/2009
Pham Xuan Duong
Hinh 9. Phan bd trudng ddng ehay ting day vao mdt thdi digm eua thang 7/2009 Sif hinh thanh va phat trien viing xoay trong v{nh Thai Lan:
Viing nudc trong vinh Thai Lan ed tga dg khoang lOl" -, 104%, 8,5° - lO"^ (hinh 10) thudng hay xu5t hign khu v\re nudc xoay dugc hinh thanh va phat tiign bdi che dg thiiy ddng luc phiic tgp va dia hinh dudng bd vinh tao nen. Qua tiinh hinh thanh khu vuc nudc xoay nay cd thg dugc ly giai nhu sau:
Do bdi dia hinh bd vinh Thai Lan cd miii Ca Mau (Viet Nam) tao cho dudng bd phia BSc vinh ed hinh dgng cong lom ve phia bac. Ddng nudc chay ven theo miii Ca Mau chay vao vjnh gay ap lire day ddng nudc chay ven bd phia Bac lech hudng chay ra gifla vjnh. Ddng nudc nay cung cd tac dgng lai vdi ddng nudc tii mui Ca Mau vao lam ca hai ddng nudc nay ph^
ldn nudc chay ra gifla vjnh, phSn nhd hon chay vao bd. Ddng nudc ehay ra gifla vinh Igi chiu tac dgng ciia ddng ehay ven bd phia Nara vjnh tae dgng lam cho ddng nay mgt phkn l^ch hudng din ed xu hudng chay Ign dinh vjnh.
Hinh dang phSn tren cua vinh Thai Lan g^n nhu la ntia hinh tron do vgy nudc bi hiit nu6c manh hinh thanh ddng chay vao vjnh men theo dudng bd eong trdn cua vinh Thai Lan cd dgng mgt ludng ddng chay cong tti Tay sang dong.
Chu trinh nay tigp tuc cho dgn khi ddng nudc ven bd tti mui Ca Mau manh ehiem uu thg tuygt ddi hoac yeu thg bi ddng ven bd phia BSc lan at.
Hinh 10. So do hinh thanh vCing xoay tiong vinh Thai Lan
Mo phong hg dong chay viing bign Nam Eg ...
Cac d$c diem gidng nhau v^ khac nhau cua trudng ddng chay trong mua mira va miia kho
GiSng nhau
Trudng ddng chay d nhieu thdi diem khae nhau tao nen bdi cac trudng gid Dong Bdc (mua kho) vd tru&ng gio Tdy Nam (miia mua) cd the tgo ra khu vvc xoay tiong vjnh Thai Lan.
Hau het cac trudng vec to ddng chay vao nhieu thdi diem cua tat ea cae trudng gid deu thay cd ddng ven bd trong viing nghign ciiu, tuy nhign toe do ddng manh ygu khae nhau tiiy theo miia.
Trudng cac vector ddng chay cua viing nghien euu ludn phan chia thanh cac khu vuc rd ret cd hudng ddng rat khac nhau va tdc do ciing khac bigt nhau.
Khde nhau
Nhin chung, trong miia khac nhau trudng ddng chay cua vung nghign ctiu mang tinh dgc trung rigng cho tting mua:
T6C dd ddng chay vao miia mua tai viing cua sdng Me Kdng cd toe dg ddng Idn ban rat nhieu (c\rc dai khoang 300 em/s) so vdi tdc dg ddng chay tai dd vao mua khd (toe dg evrc dgi khoang 100 cm/s).
Vao mua mua, khu vuc xoay trong vinh Thai Lan thudng xu3t hign nhigu hon va manh hon vao miia khd.
Vi tii ddng chay ven bd (BSc - Nam) tiong mua mua xa bd hon ddng chay ven bd (Nam Ign Bac) vao miia khd.
Kiim chung
Vai dao dQng m^fc nudc bien
Kigm chting md hinh vdi so lieu do dgc thuc te trong viing. Sd ligu dg kigm chung Igi md hinh chung tdi da tien hanh thu thgp sd ligu dao dgng mue nude tgi viing Vung Tau (Viet Nam), eae ket qua so sanh cho thay md hinh eho ket qua dao dgng mue nude khdng qua khae biet vdi th\rc do (hinh 11).
Vdi so lieu do dgc ddi ngay ve dong chay Theo so ligu do dae ve ddng chay mdi day eiia Vign Hai duong hgc duge thyc hien d viing eua sdng Me Kdng vao thang thang 8/2009 (tu 24 - 29/8/2009) va so ligu tmh toan lay ra tai ting giira ciia diem tuang ting vdl trgm thuc do lign tuc 7 ngay dgm, kgt quagiua do dae va tfnh toan khdng qua khae bigt (hinh 12).
Hinh 11. So sanh dao dgng mue nude gitia do dac (dudi) va tinh toan (tien)
Hinh 12. So sanh tan su5t xuat hign ddng chay gifla do dgc (trai) va tinh toan (phai) KET LUAN VA KIEN NGHI
vao miia gid Ddng Bac, vung bien Nam Bg xuat hien ddng chay dge bd (hudng Ddng BSc xuong Tay Nam) do nudc vao vinh Thai Lan dSy ddng chay ven bd d day ra giua vjnh va tgo thanh khu vuc xoay d vung tu vT do 9° tid len.
(5 miia gid Tay Nam, hien tugng nay ciing xuat hign nhung vdl t§n xuat thap va ngugc hudng ddng chay trong mua gid Ddng Bae.
Cac ket qua tinh toan cho vung bien Nam Bg - vinh Thai Lan nhin chung la hgp ly v6 mgt dinh tinh va da gdp phan phan anh dugc phan nao btie tranh chung ve hg ddng chay d vung bien nay.
So ligu do dgc d vimg nghien ctiu ehua cd nhieu va khdng dong bg cho nen vi?c su dyng sd li?u nay lam dau vao het siic han ehe va dung sd II9U do de higu chinh va kiem djnh md hinh Cling rat khd khan, eho ngn cac kgt qua cdn chua that phii hgp vdi diln bien thyc te. Vi
Pham XuSn Duong
vgy, nghien citii sau hon nua che dg dgng lire tiong viing n ^ i e n ciiu can ed sd ligu do dac chi tiet, day du dii hon de cho md hinh sii dyng eho ket qua tdt nhat.
TAI LIEU THAM KHAO
1. Phgm Xuan Duang, 2012. "Nghign ciru hoan luu viing vinh Binh Cang - Nha Trang bang md hinh so tri". Lu§n an tien sT dia ly, Vign khoa hgc Khi tugng, Thuy van va Mdi trudng. Ha Ngi.
2. Phgm Vdn Hudn, 1996. "Vg eo ehg hinh thanh nhflng hign tugng thiiy tiigu phuc tap va dgc dao d bign Ddng". Tap ehi Khoa hoc, Dai hgc Qudc gia Ha Ngi, tap XII, so l.Tr. 33-39.
3. Chao Z. Z, Li, J C. Kindle. J D. Paduan, andF. P. Chavez, 2003. A high - resolution surface vector wind product for coastal oceans: Blending satellite scatterometer measurements with regional mesoscale atmospheric model simulations, 2003:
Geophys. Res. Lett., 30(1) 1013, doi:10.1029/2002GL015729, 2003 4. Coo. Mellor. G.L. and A.F. Blumberg,
1985. "Modeling Vertical and Horizontal
Viscosity and the Sigma rdinate System", Mon. Wea. Rev., 113,1379-1383.
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Gov. Printing Office, Wash., D.C.
6. Marchesiello, P., J. C. McWilliams, and A.
Shchepetkln, 2001. Open boundary conditions for long-term integrations of regional oceanic models. Ocean Modelling, 3,1-20.
7. Vreugdenhil, C. B., 1998. Numerical Methods for Shallow - Water Flow, Kluwer Academic Publishers, Netherlands.
8. Shchepetkln, A. P.. and J. C. McWilliams, 2003a. A method for computing horizontal pressure-gradient force in an ocean model with a non-aligned vertical coordinate, Joumal of Geophysical, 108, 3090, Doi:
10.1029/2001 JC0011049.
9. Shchepetkln, A., and J. C. McWilliams, 2003b. The Regional Oceanic Modeling System: A split-explicit, free-surface, topography-following-coordinate ocean model, Joumal of Geophysical, 108, 3268, doi: 10.1029/2002 JC001443.
Mo phong he dong ehay viing bien Nam Bp .
MODELING CURRENT SYSTEM IN SOUTH VIET NAM WATERS- GULF OF THAILAND
Pham Xuan Duong Institute of Oceanography-VAST
ABSTRACT: This paper presents some results of the study on circulation regime of the South Vietnam waters-Gulf of Thailand during northeast monsoon (dry season) and southwest monsoon (raiiry season) by ROMS model Parameters of meteorological, tide, radiation, evaporation were taken from the global ocean data (resolution of '/^ degrees) The study results showed that during northeast monsoon, it's appeared the currents along the coast of South Vietnam waters fi-om northeast to southwest. They pour into the Gulf of Thailand with high frequencies, and push the coastal flows into the middle areas of Gulf By this aspect, the flow field in the Gulf of Thailand forms a closed cycle in the upper area from latitude i^N at many moments. During the southwest monsoon, this phenomenon is also appears, but lower frequency, and the direction of flow from southwest to northeast
Keywords: Current system. Northeast monsoon. Southwest monsoon, closed cycle.
