coastal-trapped waves and wind-driven currents over the continental shelf
TRANSCRIPT
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993 39y y s [ s s
COASTATRAED WAVES
AND WINDDRIVN
U H
ONTINNTA HF
K H Brink
rm o hyc cogrhy ood Ho cogrhcuo ood Ho chu 0543
KEY WODS: ocean-urent vaiabiity, wnd diving coastal oceanogaphalogo poagao
OO
Th 90 w rmrkb dvom h udrdg o wddrv curr vrby ovr h co h owg (190o ummrz y o h ko o our curr udrdg of hubc Sc 190 our udrg o uch roc h bco good d mor ohcd cy rm of cordwvhory c h o h b rchd whr mod d obrvo
r ow o comrd wh rob xco o quvgrm Aog h wy om xcg w hyc gh hv ob gd hu m my o rv h robm o wddrvvrby ovr h co h d hror h r org dd o b couo o A (190 org rvw
h oowg mr ocu my o vrby hvg m cog h dy bu o mo h w w c mr md o mh h ro bw horc coc dobrvd bhvor h co oc Th roch o ddr wr
coum mod whch odbc c wh o r ro of ovrwhmg morc h h cco drmcprobm xrd rm o cordwv hory r rd
390049/91/0159$000
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390 RIrs oowd b consdron o sochsc mods h m or m nob cnrd on wv mods cnr ocs on cosrdwvhor s ror bcs hs rovn o b vrs rochdng sccss rdcons s w s hsc nsgh
COASTAL-TRAPPED-WAVE MODELS
1 ntroduction
n scs o wnd-drvn vrb ovr h connn mrgn cnb nd n rms o h rors o cos-rd wvs connn mrgns ow h xsnc o sch wvs nd h sns oongshor hs rogon s ws sch h h cos s on h rgh
( whn ookng n h drcon o hs rogon n h Norhrn(ohrn mshr ch wvs gnr hv rods ongr hnh nr rod so h h on ro n h rsons o hocn o moshrc whr chngs whch c hv m scso w ds Th wvs morn bcs h r rd xcdnd hrogh hr rogon srd h ocns rsons n h ongre ren n rn we rere e een eb Hhnnc (19
FrutnBor rocdng o h rors o r cosrd wvs ss o consdr h mhmc ormon o h robm Thnrd ons o moon or srd Bossns ocn r
u v = - !P P
vju
P+ P P
nd
(
(b
(c
(d
(
whr
u vnd r h voc comonns n h x nd drcons
rscv Th oros rmr s( = 2Q sn whr Q s h rh'sroon r nd s d h ccron d o grv s g hrssr rrbon s nd dns s wrn s
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WIDDE CUES OE E SE 31
++( whr h horon comonn of urbun r V nd w b ndd o rrn wnd drvng nd h boomcon dg ubcr wh c o ndndn vb rn dnon h oho nd uwd dcon no b x nd cvy
n h bnc o urbun r rghorwrd o rduc hym (1 o h vorcy uon
J2 02)pzt\ Pxxt+yy + N
= (2
h buoyny uny ud
N =
(3
h vorcy uon o b ovd ubc o no om ow hco
Pp = x = 0 r urc
Nz P 0no ow hrough h boom
nd bounddn r om co
x 0 r co-rd wv r umd o hv h ormp [(+(
(4
(4b
(4d)
(5)
wh h dh hr chon o b uncon ony o dnc oho h h h obm h now bn ducd o gvn onghowvnumb o n gnvu obm o ( nd Evn whh mcon nyc ouon o (2 ubc o (4 r vry
dcu o nd hu uuy ound numcy v onnc ron (ng oor 1 Brn or nr ron (uhnnc1 omur rogrm or obnng mod rucur nd rd
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392 RIKproprt (dcrbd b rk & Chpm 19 r r vb dcovr a ar brod rg o ratc tuto
Stm (2 c b mpd th ogwv mt whr oghor c r rg tv to coh ca 8/8 8/8 dwhr rquc r ow 0/0 I th ca th probm bcomprb d
2(Pzt)Pxx+f N z 0Pfpy = t = 0
+ p t z 0gf()hfPY) t h
ad
P0 a X
h outo c b wrtt
l x zwhr
(a
(b
c
(d
(
(7a
(b
Th gvu o th probm ow em d mmbr o th compt t(Cark 9 o ucto Fn r orthoo ubc to
fbnm FnFmdlx=o rhxFnFmdlz=-(x),h o (wh nm th Krockr dta Th partcur ormato mpd b( mut b ud ordr to corv rg th wv propagtthrough a ow varg mdum (Brk 199
It trahtorwrd th owv mt to ov or th wdorcdprobm (wth o bottom tr urthr t rqut aumd that
orcg o through aoghor wd tr that do ot var th croh drcto [X 0 J Jy t I th c th prur ct b xprd trm o th gucto
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WI E OE HE HELF 393
where ow he amue fuco obey
(9b)
Here s he aoghore w ress a he surface a
(9c)
s he coug coece of moe o he w sress f he surface mxeayer s emay h (ee, for exame arke 1977).
scag of 2) ea o a sracao arameer (Burger umber
where H, a are yca vaue of eh buoyacy freuecya crosshef horoa scae reecvey Th mesoes umberexree he reave regh of racao aeravey ca behough of as he rao of he era Rossby rau of eformao o he
horzoa egh scae The baroroc (usrae m of (2), e 0ea o he owe orer vorcy baace
(0
ha ha he verca veocy oe o vary wh eh h barorocm he ow s he escrbe by (0 (b a (c (eg are Br985)
he foowg he roeres of he free moes are rs reae heexcao of coaarae waves s he cosere a ay comaros of moe wh observaos are scusse
3 FrWv Prrts
he geera roeres of free coaa-rae waves are ummarze ceyby Huhace (975, 978) a by arke (977) For arbrary oograhy a racao here a free-wave moe mar o he baro
roc Kev wave us a e se of hgher moe ore owyroagag wave of hee wave moe have hase roagao he ese escrbe above (eco 2), rove he eh creaemooocay wh ace from he coa ower (hgher orer moe
Annu.Rev.
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39 K
hv possivy mo omp spi ss (i ). I h dphinrs is no monooni hn n inni nmbr o wvs wi so xissppord by h rvrs sops ssoid or xmp wh rnhs(Mysk 979 Mysk & imo 19 Brink 193 or by bnks(Brink 19b Inrsin h sriion rss n n inrsd rny (hn phs spd or ivn wv mod. rhr mkin hiid id ssmpion [nin h divn d o h dispmn oh r sr . sn pz = 0 in o (b] ds o n inrsd phsspd
In h broropi imi (Hhnn 975 whr sriion n bnd -wv mods is o onsho wvnmbrs bxp or h broropi Kvin wv hir rnis r wys ss
hn h inri rny (i..
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INDDRIVEN RREN VER HE HE 39
Sa ss us f a a sd ns a f saa dashd ns
h v runcy incr uni i rch h inril runcy (hlins in iur 2) Huhnnc (19 h hon h h v uncyil rac! i te aium value o
A 17 :I,
11)
vud h boo is greater tan or equal to unity Once a dispersioncurve rises above strictly trapped waves apparently no longer exist.
hysiclly hi ould occur bcu h col v bco stronglycoupled, troug te topography to te continuum o freely radiating
oceanic internal waves Tus te coastal-trapped waves ar apparently"leaky in h sae sense as are edge waves (eg Capman 192 In telimit as te continental argin is uc tinner tn a typiclinternal Rossby radius o doration and te beavior o te wave
modes s lke tat o pure internal Kelvin waves (. Gill Clare 1974Once a dispersion curve reaces te wave's group velocity is generallyin te sae direction as te pase velocity or all wavenubers were te
wave eists Tis substanially canges te nature o scattering o oopogrphic obstacles since reection o energy is no longer possibleWilkin 19
ufu diagnostic or a given v o is te ratio averaged over awave period) bn kinetic eergy and potential energy P
= P (12)Brin 192. Te ponil nry i h u o two coponents: One is
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39 RK
ssocitd with th discmnt o h r src P nd th othr isssocitd with th vrtic discmnt o wtr rcs in strtidocn PJ In n nstrtid ocn Ps = 0 nd P is sm comrd with (ct or th brotroic Kvin wv so
or shwv mods In ct in th iidid imit w hv
gH(fL)-2
(3
(
(b
In th oosit imit o Kvin wvty bhvior (r w hv
nd th imortnc o rvity s rstorin orc ows th irtitiono wv nry Onc scic wv mod is cctd it is strihtorwrd to stimt f P nd P nd hs stimt th imortnc obrocinic cts.
h snc o mn onsho ow ov th continnt mincn tr th rwv rortis throh or shitin modictiono th bckrond vorticity d nd by owin th rowth o inst
biitis h cs o brotroic stb costtrd wvs hs bntrtd by Brooks & Moors (977 who wr inrstd in h ct oth nrtic orid crrnt on costtrdwv rotion Lthr& Bn (9 considrd th inry nstb mods ssocitd with thG trm o th Unitd tts roin cost nd ond stoninstbiity rowin on h inshor d o th mn crrnt. hy wrb to idntiy this mod convinciny with G rm shins whichhv bn rnty obsrvd (.. Bn hn costrdwvs rot in th oosit dirction to tht o th mn cnt th
ossibiity o critic costtrd wvs riss (Gi & chmnn 979his is sittion in which th dirction o wv rotion is ocyvrsd owin to th strnth o th mn ow Gi & chmnn (979rst risd this ossibiity to in th obsrvd bsnc o costtrdwv rotion o h N cost whr h hs crrntcoms rticry cos to shor (.. chmnn & Brink 990 It nowsm mor iy h h bsnc o rotion is rtd to nhncdriction dmin ssocid wih th distortion o th wvs modstrct by th mn-ow vorticity d (Bink 99
I rs ht th min mchnism or th dcy o costtrdwv nry is bottom riction It is strihtorwrd to incd its csin th onwv imit whr th dcy o wv mods is ccomnid by
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39 BRINK
i
W5m
5m
m
em/sc +E
ifid
Sf W Sm d
F Resuls of ting oastal-trappedwave modes to dirnal tide data from he shelf Bii Clmbi ( Cwd & Tm 1984). T cnt cii fmdnt modld w nd thr m a hown, od nt llip
( whih rds h probm omp wih boom srss o n innis o opd ons
c; t-y+ La , (whr is h mpid o wv mod h riion opin oins r dnd s
(b
whr sbsrip B rrs o niy vd h boom[ = (] nd is a onsn o proporioy bw boomsrss nd boom voiy . n h imi o w riion hions ivn by (1 bom nopd ows ordr nd nb hoh o s n invrs-dy disn or h r wv
h phys mhnism or h wv orin is srihorwrd nonshor wind srss ss n onshoroshor rnspor wihin hsr Ekmn yr n ordr o onsrv mss ompnsin oshor
onshor ow ms k p rr dph. s his ow ross isobhsvorx srhin ds o hns in h o riv voiiy. hisvoriy is xprssd ry in rms o h onshor voiy n
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WIND-DRIVEN CURRENTS OVER THE SHELF \ 3i te preece f agre ariaiit ( ) gie rie t waeroagatio
umer f practica quetio ari we oig coata-traedwae rem (6 ad a) Firt, we cmputig the freewae moda
tructure there i e queti aut where t pace a articia erticacata wa Such a aritrar udar i ued to excude te ighturuet ier hef that the iicid free-wae equati (6) remaiaid hi proem wa addreed Mitchum & arke (86a) whohwed tha a reaae cice i t pace the cat at the iatwere te water deth i three time te cae thicke of the turuet(Eka) udar aer I additi te hwed that the wid tiexcite mti withi the earore wedge o that a crrecti (oe
ma) to the wae reut proportia t the oca agore wid tremut e added to the wae outio' coata" ea ee i rder to achieeaccurac Their reut are depedet a high ideaied frmuati fthe ottom tre ut ethee aear to work we i practice (Mitchum& arke 86)
ecd qetio ta oe arie i ow ma mode eed t eummed i order to achiee accurate reut [ie what i the rage of i()?] Ear aicati f coata-trappedwae ther ieded adequateto er good reut with o a ige mode (rik 18 attiti & icke
8). arke & Va rder ( 86) te ther had argued that eer mre mode tica eed t e ued i order t tai accurate reuteecia for aghre eocit. hapma (187) addreed thi quetioi the ctext of hidcatig curret o orther aiforia ad cocuded that mpremet i the hidcat ccurred whe mre thathree mde were ued. I reaitic tratied ituati te accurate cmputati f higher mde ted t ie ciderae epee thiiue i f ome practica imortace ope & arke (18) foud auti t ti dicut ticig that for igher mode ma) (a)reduce to
C; Ynt+ nmYm b;r. (16)mn ter wrd aogore ariaiit (ad hece wae roagatio)ecome uimortat. Loez & arke (8) the rped the fowigaprac irt e for reure (which cerge fater tha ecit)for te rt ew wae mde uig (1a) Ti ifrmati i te uedt precrie i te (6) whic i the ed fr ta preurehi metd aid the dicut cacuat f higher mde ad ridea ratia eparati etwee ca" ad remte frced" uctuatiThe remote frced iformatio i tat which woud e otaied from
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400 RNK
sng (1) (e. drec usng wnds frm rge sp dmn) ndhe c rced nrmn s h whch cud e ned rm (16)r equen he resdu he Lpez & Crke (18) meh.
Csppewe her ha oen proved quite uccesfu in prc
ce Fr exmpe s & cke ( 84) nd Chpmn ( 87) heused demnsre h rge prn f he seee n ngshrecurren r he wesern Uned Ses s ssce w wndforced oaarapped wave Tpica reut are shwn in gure 4. Thewnd frcng ccurs ng he enre cs u s ms eece where hewnds re snges, nrhern Cfrn her successfu ppcnsf he her he een crre u fr he shef es f Ausr (hurche 86) nd he wes Frd shef (Mchum & Crke 86) s fr s h n n cs regn where edence f csrppedwephenomenahs been eriou ought, i ha been found There s, however cnssen prem Ahugh h we her wrks que we frhndcsng pressure nd he ngshre cmpnen f curren, hse r n sk hndcsng dens r nshreshre currens (egChpmn 187). Sme reaon r hs paria faiure are dscussed inSen he uf f frn mgh pre e n ecepn n hpremnr resus sugges h susn pr he emperurer here s reed we prpgn (Merred Wnn
18)Ms sudes f cs-rppedwe genern n nure ne heuse f dnmc mde hs ppch mpses s n he sud f s s desre seek mre emprc pprches One such erwa made y Chapman e al 188) who howed ha for hindcaing eaee gen wnd d er sp dmn dnmc mde sed n 5 wrks whn errr s we s n enre ssc pprch fr heregn shre f nrhern frn hs n eec ss h he rsorder wave-equaion mode work abou s we a an poibe inear
model, given he inpu more ambiiou, pure emprc es csrppedwe heor
ws underken Ds & gden (8) he k he pprch frng expn cenc r er he shef nrhern rn usng rge sue f wnd nd seee nfrmn s npus hefound ha a large par of he ealevel varaion o Calforna a oherennd n phse resu h he ene dened s rrpc Kenwe unknwn rgn. he resu se-ee rn ehe rges wud e expeced csrpped wes. he fund h currens
ner were nuenced hs we c n pure c wnfrcng he c frcng cnriued n n gshre cures us he nshre curren cmpnen nd emperure rns
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g v i gh e) (hay ne) h i al hl h ala (i i f Cp 1987) a B (i ba f h i hf (2 a h ih 3); () h vci (i i ) f h hl 20 (C) hlf 55 C3) a h h 90 (C4)
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40 BRI
Oell he esuls e onssenwh hose h h be epeed osl-ppdw he bu he h h ddd bn plnngoe ne hn we-pe odels he been ble o onle
p hs pn he dsussn hs used n h en slpped wes b le-sle lonshoe wnds Ohe possbles enl exs. Fo exple Webse & ollnd (187) deeloped equendon nlue o (15) h n be used o sole o wndoedmns n equen Gdn & uhnne (18) pd pulnn h d beh n he e gup el he eebp wes nd shwed hw sllng uens n be geneedn epne wnd pulse The esuls expln obseed uenns he h Se nd hs qlel n sme h
bl n nsheshe w e e uene n ems sl-pped-we mdelng.Ohe mens ng slpped wes d n nle he wnd
sess del Fo exple Kol & le (176) nd subsequenlohes he expled he possbl h uuons n he dludedeep en de shel wes o onnn obseonl edene osuh excitaion has n nd. Th situation a lw latitudes,hwee, s deen The equ s s w gude whh s neuped he ss A he esen edge he en bsn nmng equl
we eneg n ehe be eeed o nsed plewd lng hes n he slppd wes (Me 168 Ck 18)Eneld e l (87) used obseons o ke nnng se hequl Yn (med ssb-g) wes ee he bseed (Smh178 Cneoodgue & Eneld 8) ee sl-pped-we Peu
Ss o esues epesen nohe neesn neupon o heosl we gude. A good exmple s poded b he ee o udsonB nd he udsn S n w h Lbd shl. Wgh l
(18) demnsed h hnges n pessue e he b led ues u he s nd n he Lbd shel. A he shelsunn he osl ux bees nlgous o wnd sess (Mddlen88) n ng wes e he shel. Anhe neesng exmple s ho Bss , beween nlnd Ausl nd Tsn ppes hlngs wnds gn ws whn h s whh n un eslpped wes h popge nhwd lng he sen s Ausl (Clk 18 Buhwld & Khn 18) hs eplnno he ogn o he nohwdppgn wes lees ne neesnquesn peul o hs pble unnswed: Whe ds he eswdopn ene lon he Ausln suh os o? Chuh & Fee
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WNDDRVN CURRNTS OVR S
and ( 8 mad a cnincing ca a i d n pa arund Tamaniaand ark ( 8 sowd tat it cannot pass trug a Strait t smspi ta t wa ar catrd in t pn ocan a t pa tarp and pgrapica cmpx urn ip f Tamania
25 Summry
oasta-trappd-wa tor proids a powrfu concptua mcanismfr undranding argca w r continnta f. T undring ida f wind-drin ariaii prpagaing in dirctin f caatrappdwa pa ocit i cncpua imp and a nrid rpad rain. T r wrk for prur(sa ad aongsor ocit, and on rar sows an usfu ski
for dnsit r onsor ocit Tis ack of ski is praps not surprisingin ig f t tndnc fr ord nr currn iat ngwa aumpion ir magnud and aing rt pata casrai angr ci (.g. undu & n 6
3 STOAST MOELS OF WNRVENRRENTS
T md dicud in priu cion a a cmmn radof drminim Ta i a, t cud ud, gin tim ri finpu, o produc im ri of upu a can n cmpardwi ran Anr apprac caic n u statistics f input functions to indcast t statistics of t osrd ariaii Ti apprac i in m wa, mor cmpac and or mpica ngt ta mig n rwi o oiou
3 vB M
An & Dno ( 8 took adantag of t fact tat t ongwa windforcd prm cud simpid to ( in ordr to instigat taiic f windfrcd rpn T furr aumd ta n aing wa mod i ndd Wi i aumpin ma nw m a tna i appard qu aona gin infrmatin aaia a tatim (g Bii cc 8 r ca f a ing md r wrr ar mutip, uncoupd md (i. anm = if " ouionf ( i
YnCy,t) = cnbnf exp(-cal)'o[(y+c)(1)]dl (
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0 BRI
o n innt tnt o cot nc thi oution i nown i bcotihtod to d covinc btwn t dintoction nd btwn n nd h wind t o h ovrincdend on uon the od coecint
bm emnd ann) nd uon th
d utocovrinc unction o th windt ocin hich i prued knon
Tyc eut o th n & nbo (19) ccution r hown inur The uoorreon unon o ind re (; no hon ued nu o h od I ud o hv t jor nd inor on h o th pot iniyn h hr i no prrred endncyor nd uuion o prope onhoe The uppe pne o iure
1
p E 6
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2
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ge Tl s s snl- w ss n 988 Tp ln s l ih s YL im IL . ttm m fo oo o l (0 0 h w r im ls
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WIDDRIVE CURRE OVER THE HELF 40
how he reded aoorrelaon fnon of ea leel pp (or angle mode he fnon for alonghore elo denal) The l ofhe elle ndae alonghore roagaon of he gnal n he ene ofeewae roagaon. The loe o he majo ax o he ellal on
or repreen a ale nermedae eween he phae eed of heforng (nne n h ae) and of he free oaalraed wae Inonra he orrelaon eween wnd and rere Tp (oom anel) no o mmer The maxmm wndrere orrelaon or a aloaon eam h egad o wae oagaon. e loaon o hemamm oelaon le on a agh lne ang hogh he ogn andhang a loe exal eqal o he freewae roagaon eed. The Allen& Deno (98 rel are er powerfl n ha he an readl eoared h oered a. Perha mo nereng from an oeraonal andon he ndng ha rere (or alonghore elo)hold e e oelaed wh nonloal wnd an e ha ndeedoered n nare e.g. allwell & Allen 84 Wnan e al 98
he Alle Deno ( 84) anal ha een eended o he ae hmlle mode haman e al (1988 Two anal hange orwh h generalzaon. r he orrelaon dagram eome fnono loaon and o aale. Th follo eae
= j- 1 L YnF.X, znand eae he modal fnon ae deen for eah Alo he lo he maor axe o he oelaon dagam a o a o eeena eghed modal e) aeage o he hae eed o he eemode hamn e al ( 88) ed hee rel o how ha hreemodeorrelaon dagram elded areal eer heoreal rel han
nglemode dagram when omared h oeraon made o norhern alforna.
32 More omplee Models
The Allen & Deno (198 oha aroah, ed wh man mode,n rnle eld orre el for a road ange of rolem whee helongwae lm ale and orng on o onl an alonghore wndre ndeenden o ohelf dane. Th aoah, hle erenlghenng h omeha lmed n alal. A oe geneal
aroah o he lnea olem made relaxng hee amonn h ae he aoah ed o oe anfom he eqaon of
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406 RINK
moion (1 wih repec o boh ime nd longhore direcion Thi lee twodimenionl boundlue poblem to be oled o ech equenc nd longhore wenumber (pilne 1980, rin t l 1987eldng frequenc-wenumber rnfer funcon The wind forcing
ener boh the co nd he free urfce while boom friconpoide dmping mechnim The orcing o the model i precibedhrough the frequencwenumber pecrum nd the crohlf rucureo the wind te (Figue 6 One obtin ttiic elting cuent towind fnction of ( z) locion nd frequenc b inegring reuloer longhore wenumber, uing the windre pecrum weighng funcon
ome epeenttie tne unction t xed equenc e hown
n igure 7 Pronounced pie ocited with rpid phe hift (nothown, pper in he trner unction or v nd p Thee repreent thecontribuion from colrpped-we reonnce Upon inegrion,hee pie end to domine he mplude o he repone epecllince he wind pectrum red (h i h gree mpliude longwelength The phe hi ocited with hee pe, howeer ledo rltvly mll o-pr, or rlvly ow orn bwn wnd
nd v or p Thi i he mhemicl epreion of he fc h propgingenerg rrie from locion ucienl din h remoe incoheren
forcing pl unil roleThe rner uncion for onhore current nd denit re no o domined reonnce pie Indeed he fncon incree for hor clend the funcon fo hot cle Th i in dinc cont to
+-
/
b ki' )
gu rquny-ongho nm um o ongho in foh W o o h Uni uring umm 8 Uni h b 0 og o(yn m) (y k (y y) (ih mion fom ink 87)
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15' .", '
li
JR(cm- x fO}
WDDRIVE CURRES OVER HE SHE 407
2
.,.15 <
10
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8 RI
4. CRITIQUE
The abe ectn rea addre n a mted hca regme uctuatng mtn dren b ucuatng wnd n a nearzed near ncd
cntext Whe th te f mde uccefu n me regard t eaecnderae rm fr mrement It thu eem reanae t cnderre a few tc that cud nt be dcued fu here.
In the cean turuent urface and bttm undar aer amtawa ext Snce thee are tca f (1 m) thck the ccu autanta art f the hef water cumn Athugh me f the eectf thee bundar aer are accunted fr abe her cnderabe current and thema erturbatn are nt cndered Turbuent undaraer er the hef hae dnamc ha are a ea wdmenna
and hence tanta mre cmex than n mer ettng The mbu eect ccur near the urface where hrznta emerature gradent acated wth uweng can ead t the generatn f araeundaraer thckne and f nearurface frnt (de Szeke & Rchman18 Rudnck & Da 188) Lkewe w n a bttm undar aerbeneath a trated nterr and ae a ng ttm ead t uancnduced anmae n the bundaraer tructure (Weather & Martn1978) In eher cae t cear that turbuen bundar-aer rcee
er he hef and e w e cmex and are mrtant cmnentf a cmee cata-crcuatn mdern are a cmmn henmenn n he caa cean nce a frnt
frmed t adectn wnddren curren can cmcate he thermarene f the cean (eg u 18) urther the frnta drn f theambent rtct dtrutn can mdf cata-traed wae and awfr the extence f new, frntatraed mde (eg uther & Bane 18)na au te f cata frn aear t e hdrdnamcauntabe (e agg & eade 178, Narmua & Maxwrth 18
arth 18a,b, awarkewcz 8) ntabte ead t curren uctuatn that are nt drect reated t the wnd and that ma re tbe a ubtanta mechanm fr the exchange f waer and matera acrthe cntnena margn
Addeg he rem f tead wnddren current er the cntnenta margn at rt eem t e a me a takng the tead mt f(1). Th t true nce he reutng uren f the ertca ect(e) w the ead t nguarte Thu t necear t add new hct n tea, trated mde. ne arach ha een t add hrznta
and ertca mxng, a rcedure that ead t reut hat can e uaate thght f a the tead mt f catatraed-wae generatn(Mcrear & ha 8) Ahugh wnddren arab whetherremte r ca eem dmnae anghre curren uctuatn er
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WRVE CURRETS OVER HE SHE 409
h hl, no clar ha ady wnd lay a mlarly domnanrol. Varou nunc o h d ocan on h hl canno b nrlydcound Huhnanc 984, cCrary al 986, Klly & Chaman988, and uarn ouow can alo drv alonghor currn (.g.
Barly & ar 97 an coaalra wav (hha haman 98 urhr nonlnar roc can lad o h gnraon of aman ow drvn by ucuang currn (Lodr 980, Hadvol & rn98, Samlon & Alln 987 I , n ac dcul o u obrvaono modl o man currn. Th o, a la arly, bcu habnc o ucuaon (by dnon o man" ml only on ralaon an hnc oo fw gr of from o mak any manngfulacal
5. CONCLUSIONS
I woul canly b ar o conclud ha w hav dvlod a ohcad undrandng (and rdcv caably or varaon n alvl an alonghor currn ovr h connnal hlf for ycal rorangng rom h nral rod ou o abou 2 day D h mrv rul o n modl (g. ur 4, hr ar ll om roublom roblm r, ng modl nd o undrrdc h amludo obrvd ucuaon o alonghor currn and a lvl ycally byabou 0%. Scond uch modl nd o undrma roly hobrv ngh of ny an cro-hl currn chang h lardculy aar o b a la arly aocad wh h longwavaumo whch ur h mall aal cal ha yy acualcrohlf currn. ny o h roblm coul alo b rla o fronal,nonlnar or urbuln roc ha ar no nclu lcly n mong wnddrvn modl.
Our rn undrandng of currn ovr h connnal hlf whl
ayng om rgard clarly nadqua Th o bcau manyroblm o nr, uch a ocanc ronon, coaal uwlln andh ral o olluan, nvolv h chang o ror acro hconnnal margn. Undrandng ranor acro h connnalmargn rur an undrandng of onhorohor currn. Such anunranng rnly lackng an lkly o b h focu of condrabl rarch n h comn yar
ACKOWEGMES
Davd Chaman and Svn Ln rovdd valuabl commn Suoror h or wa rovdd by h Oc o Naval Rarch (ONRhrouh h Coaal Scnc roram, cod S
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410 BRINK
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