DTIC ADA430133: Modeling Ocean Deep Convection

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by  Defense Technical Information Center

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fre os the LDO resin,

Oceen Medline, Deep Conserion,Fwbelence Models

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Modelling

ELSEVIER ‘seu Madalng #2004) 15-95,

Modeling ocean deep convection

‘VM, Canuto ***, A, Howard **, P, Hogan €, ¥. Cheng *, M.S. Dubovikov §,
LM. Montenegro *

* RASA Gnd butt for Space Std, 2880 Boat, Nov York, BY 1025, USA

® naparsne ah Appel Pgs and Seaton. Contes Unser, New York NY 10077, Sa
of Ea, Atonplric and Pencany Seonts, SOT. Carbvdge, 344 OT, O84

Nemt Roser Faber. Suet Space Gey, ES 38529, TSA

«Deport of Pit, HCE: CORY, ew Bark AY HD4S, US

The gol af thes et assoc ns for Bp Cacti wlth spate
renolaion ocean poner culation navi, A niodel fr ep convection tau: contain both Yert el
Transport aad Casrel advection by msoocile eddies generated hy hazaelini invabiis, The rst proces
‘operates mostly in ube inl paces while the cozand donsnatcs the ial steges, Hee, the expe i om
fodeh [or verlkal wining, Whun ncanscaler are aoe vealed, chey age treated with he Gen md
MeWlFsens partmetrfnrinr, The rand: rovubswe tested ageinl the mensusuteas of Lande, Dees
‘as Outre, 2902 (LO) in the Labrador Seu. Specially, ve sll inyuire Whether the mnt are ale to
reproduce le seston oF “aeaateomoetin” which we shall ele 10 as DC (aise layer apts RO0-1 300
tap. Ube eogina where wn rseauned by Laeoder ef (2002) wil be relee va lle UDO region, The
mo roses of thie study can bz summarized us tollows

(0) 3°43" reroos, A GEDL-ype OGM withthe GIS8 vetien eviring reads prodics DC tn the LDO
region fess the verti hse! stl is uae lo be 10 rs 2, val ati quite clos co the on
suggested by heuristic studies, No parualt wae csry fcun the nigil GSS rood. Hovrever, he
GASS miode aio price soune 9G fn 4 tepinn eo the cst athe LDO cesion

(2) 3° remation. A GEDLAype OGCM wil th KPP mode everything ce belug the sam} doesnot
Dretit DC fa the LOO reiou ster Ov slit hear aus fund ta Be 0.5 1C~" ane” bch is
{he backysound value, Fhe KEP model yale DC any t the cast ofthe LDO revion

(8) IPT resntion ntact, MYDS nsing ehettepredets DCin the LDO cepion. However, ialao
predins DC tothe weet, north wud south of i, slag ii cle. The hhaviee of te KP and
‘MY modals ate some wnibsymamrce, The BY seals yield toc Tow a mixing i eably sratiied

*Coneporaieg pvtor. Adlscve NASA, Cosa lait fr Spaos Studs, 2380 Brox
Me, USA ede <1 2 40835Me fs #1 RUD HS
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Mew York, NY

2-500 se fou ner 3 2204 Ther FA ight nate,

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" EM, Gata. Osun Atodng 7 (200175 95

‘ows since they predict xe) Riche:dsou winner Mier) 0.19 whieh eve les stellar than the
‘ahs ie) = O20 needed (o ubtsinsealstis Ml. depts, Howeser, as discussed uhuve, in unstable
ratfcations the MY sacle el beter alls, Oath over Hand, the KPP move, ich was mo-
tivated primary by the ogee» overcome the MIV "ton low mixing” in sable scien, yielcs ut
nie Tslutin, 9 DE it the LDO region, In this respoce, che GISS motel yids oth comet
Ine] = O(1} m stable tification ond cores tests Inthe usable vunlgutvian in che LDO
exten

(6) TAU revouton Jn his uve, RPP predic tsa Saye depts upto 1.7 om inside le 2100 rosin
‘whee ar coarse resolution nune exved Haver, the ate sl prnduoss DU al locatious outs che
LLL seon where it isnot abservad. Hoeven, tino these rpions are interning! wth wiry sallow
‘rive "ayer depth, the resuling sen mead Iyer depts les auto be tos than #60 m bios evry
‘where oteids the LDO ceginn

(6 1/}200 I revatio, Tr fhe cane, KEP prese!s ied ayer dspts up ty 3 km both inside and ous
sie the LDO reo, These regions ure, Seve lao, Inrovingled wth very shalloar mised layer eps
‘ith remdg mem saned dapohs gees tha 200 ro bach nade and vue cae LDO region.

Ti conelusion, as few mal for deep cuestion to 2 used in cose rescutin,thsse rel ince
that the GISS mang model face well wilh sevens ip beck stable and wnstabts stasieuioas bul
bvewslniatos ‘tr geographical extent. Tis fads lo the pcoblom of Zucurs imapzogesnats of the modeL 11
imu be generalized to rele the filling phyokay hugo fatures: fp rottion that Sogomss ii
perlul in the lear pases cf deep envsction wen ae © slow dawn ta rte uf red layer deepening.
(Bi melretty fa partial Sheen wih ie large (vegeta i tho init phases of doxp coavescon am
hesnoac sal inthe final stage, and finaly, (2) 1 Mee] to teat lara adestion by beredtinc elon
that inthe Hal stages of deep eonesoton vrinanss ner verdad Ieanspoet,

1 208? Lover Lt. All sight reversed

4. Totratuetion

\Barlb’s etmosphers imeructs with the covan iv two ways. Wind stress caute stoue mixing
the Bint ~100 m of the oceun (enixed layer, ML} but hardly affect water masses delow the MT.
where lies the large portion of the ocean characterized by stale sLsuiication and shus weak
tbing, To the elect of commeaiceling wilh The dosp oosan, eg, in the process of absorbing
Aomospheric COs, stable sratfeutiou acts Re a rigid Kid tkat insulates the strongly mixed MU.
from the wenkly inired deep ocean, If such a configuration always prevailed, the dsep oscan
"would be she le fran cacatie events, oop waters would be dynamicully decoupled trom mura
henomean and the coean decp currents would be considerably weaker than whal is observed.
Diferentat solar heating betwen tow und Big Tatitades would not sestlt in a poleward Dow of
‘Natt waters and the Atlant would laok ntore like ce Pacific wheee thee are no daep convective
regious (Wesver el a, 1989), Barth's cimate would be quite diferent from what is observed
today.

'Desp Convection is the anfy process Cuvagh which surface phenomena sech ex buoyancy
losses, brine rejection, ote. picrde the Bd oF strong stable stratification tha characterzes the
thermoeling, Citinately, chit leuds 10 the formation of deep waters (Chu and Gascard. 199%;
Maxovorthy, 1997; Marsbull und Schott, 1998; The Labeador Sea Deep Convection Experiment,
Pat Conan eat! Coens Hdiling 7 (00H) 79S ”

20112), Open ougam deep convection occurs in small nurcber of fovatioas, Labrador. Grcenleud,
‘Weeddel and Wester Mediterranean Sons, and yct iti one of the ocean's mnejor features since i
tepreannis the inal stage uf ie global-scale ventlation loops cf the world ocean (Sander eta,
1995) Ia fae, itis the domaincit mechanism rosponab'> for ths production of North Adantic
‘Deep Water (NADW) anal of the Antarctic Botcom Water (ABW, Weaver el al, 1999). Both
‘NADW aud AABW play a mujor rule i earths olimate

‘Loss of surface bunyuncy und/or buine selection Icad t9 a tap-heasy, wesluble eunligaration
which acts as promirsor of farbilent motion that ultintately ads to deep camvection. The late
lpwelle warmer waters chy; cin mlL ive und redtoe the albedo resulting in a “agate feabc
hat affects climate OKivorth, F9RD_ Regrettably, howoeer, deop couvtetion is still paarly
rmodsled in coarse rese'ution OGCM (Killworlh, £989). While laboratory and aomer‘ad sim-
lutions (Stade €: al, 1995; Denbe and SkylingsCad, 1986; Skyllingstad et ab. 19% Maxworthy,
1997; Macshall and Schott, 1999) have brought ligbt several key featetes of eonvoetiee pro-
cers, Une Waustation ofthis information ict a liable model for coasse resofation OGCMs has
not yet been cohieved but, given the complesty of the phenomenon, this is hardly surprising
‘Batore we test moesls for deep convection, itis impoxtant (0 escuss some ofits key features:

(I) Deep eussccton is 9 highly nobudent process. This is exhibited by the large vertical difu-
sive hy

Kaw ben (e010? cas! ‘a
where we have wed Po (1-2) ac and w-~ (1 5} cms}, we deus by Marakall a Scot
(1929), Equivalently, one ey consider the large value of the Reyaolds annber:

hem Kf ib
whore ++ 10? cmés 1s the kincmatic visesity of seawater. This, « high-Re curbulence model
‘i needed to descibe deep convective process

(2) Deep croection is affected by rotation. Consider the charactesstc‘ength seals (Gotsatin,
18805,

A eo8} + (Buff)? ~ (BAS 1.56) fom ‘)
where B, i rhe surface bunyancy and f is the Coriolis parame. ‘Phe numerical vals in (to}
correspond lo the Greealand aud Mestteransan Soas (Marshall und Schott 1999, Table 3.4.1),
Goniniry ur tke uunoshesie cage whose frat) i much larger than the height 1 kin of the
Planetary Eoundary lover, in the aecan ease the reverse is often true. namely £{tne) may he
onsiderably smaller aa the occan depth # thet, for the Ce cases just cite. is 1.5 and 1.8 kan,
‘This yields small Rossy numbers Ro = ffeot)/it — 0-03, an indication of ths importance of
rataton,

‘A turbalence model mst be ae to incerperuls rotational sects and more specially, it must
Ihe uble Lo repruduse key featniss lie the Golytin's scale (Ie). Rotation enters ihe tacbotence
fxvalions not only through te lear Corals term i the dyateanic squations for de turbulent
‘electy Out. more impartam, ieafeete the very sleus“ure af ie usu-lngar interactions tet arc at
fhe heart oftmbuenee, bn the prosence of roltion. velocity components wits diferent vectors are
rotated by the Corot fe sround vient sass that coincide with the dirccrams oF
sponding wavo-weters. Thus, tke energy eascade trom large to mall eddies ix imbiited. Ar
m A Cama a 1 ota Hasing 7 (2028) 75-95

inorial rage is stil prevent but only for ware auibers larger than &(tot) where the later is the
jnverse of Eg, (Ie). Par wave auunbers & < kot). the spectrum is no longer of the Kolmogorov
type. That is, one has two cepimes:

E> feat} Bib) ~ DPA, be pot) 2) ~ MH (1g)
where cs tte rate of exeapy dissipation. Intoguating the (ro spectra one derives that the eor-
Fesponiling velocities wilh and without rotation are derived to be

sefeot o @/etroy BLN wo ~ (BAT? {ls}
where we have non the uissipation rte x equal to the surfers buuyanoy flux #. Values of wo")
Une wey for the Meditersanenn, Labrador and Groenland Seas enn bs found in Table 341 of
Marsball and Schott (1995). carbulence model capable of predicting the wo cepimes of the
energy spectiam Cle) has acently beer. oastructed and its implcations toned against cicct
‘Bumerical sraulations (Couto and Duboviko, 1997)

{@) Deep convection cainor be fly rewesersed hy purely loool mente If, 1~ 6 a7
ocnpied by the epiduwndratts (plumes), oue has (Mien and Rotwano, 1990:

eo HID, 0-804), 3, vPP 8)
whee 5, 6 the skevest of the velocity field, | thrador Sea data (Cavender of aly 2002; Herbuut
tne Marskall 2002) show thot in th inal stages of convective deepening, 8. Targe al
rogeive wl in tho Gna stages ie onal: skewaess subsides yaih vino (or mimes vals at
Saute Table 1 af Lavender ot al, 2002) This means thal wpaafts subside wih time rnd that the
‘Sonwaed vertical veloritics acer auore frequently kan upward veleclics, By using a lace! model
with 5, = 0, or equivalent

enn cay
ate asvumes hat devindrafts nd upsrafs ovupy’the same fractional areas, thal i aocal node
oproseats only the fnel stages of doop tanwetion, Op the olker hand, the OPPS rnodel (Oss
Pensirave Plbme Solus) of Palamenie & al (1094), Palusekiowir wad Romtea (1997) rene
‘eaats th nial stages of convective pucesss, bv fat, eonsdcr dhe two asunnptions underlying
the OPPS (a) un Belated plone. Thi teats thal the fractions] aren cceupied by ch plume must
be smal

j-ael 2;
From (2) follows that 5, must be Lange an negative aud thus aplcme inode] apie only 0 the
Initial stogs of deep conwccton; (6) a guercent anaenmaene in whic the pone Is embedded. If

Teble 1
Bowie ue on pylon ofthe el aot Rael ens of Dex Convection
z % 3 a) Te
Ye Yer Re Yer ee
x he re Ne x

For eal (NE) er fain de PTs ay (AY, plone OHA PMY aa elas DONC.
YM Cato a1 Osc Modefng 7 29063 72-85 Ey

the downward plate’ velocity ise and che upras yloity s wy mass conservation demands
that

(1 s}fo=y/ng 0)
Since in the inital stages of development dowravard plun:ss have velocities some ten tines Iyer
than tke upelests, Ba, 24) impliss again (22). "Thus, both assumptions of the OPPS mod! ep
resent the semi piyecalpiotte ofa plc in the dots! stayes of development whereas fur=
bulence model vac desert al stages plotided is nao-focah at is, eapable of incorporating tho
locity fld skewness,

(8) Deep commento eo prety wera! pres. Te itil ad al stages ae charatized
‘nat only by different values of the skewness 5, bvt also by an additional important feature (Fones:
Zit Marsal, 193; Vshek et 1, 1996, Marshalland Scion, 1999 Herbace and Marshal 2003,
lavender eta, 2002. Inthe ie pes, te ned Taye Geepeus sta rat a oord wit that
agvan by varie mining madela (Vibeck tab, 1996). Homever wad ie ploue as deepsurd to
& disteace # such that 42> fol, rolaGan lnkes over aa a bagocinic instability seein, The
deepening proces pares since barovtns ees transport Quid mae away nterally. Thus
fe thelnrr stages of BC, lateral advection dorainles over vertical transport (ee Tig 6 of Vsbec.
Gal, 1996). Since Lavender ea (2002, Tig. 13} uve showa thatthe eat ot casted by he
‘ertcaplomeseannat balance the winerwrfuce Rea hs, a considerable faction of tie Rea us
Teast ho cared hy “eatures” tha have a Uf time longer ita dat of te ples Odour), Ib
Table Te highlight the relative impure of the diferent processes inte iil and al sages
of coop coc wetion

Sine ere model is apliable musty ie itil stages 0° deep conveston,t may be ait
to connect it wilk the initiulion of baroclinic instabilities that ¢ccee mostly i the final stages (LA
sinT PM esr), On tis otter hud, a urbulenoe model valid for asbiuay values of sees,
tnd rotaion it aplisblew all stages of deep couvection (TM conn). Ea ooisTusony a rele
‘dl for ap consetion erste obit of vertical meg tar oence moe wt oon

foal, tether eth a mesoscale parameterlaulie fo dsr ateral eect

and

2, Models of desp enmestion
2.1. Consortne aortas

Conveetive Adiustrent (CA) was proposed by Bryan (1969) as a temporsy scodel but its st
jn use day. 1s heen recently analyaed by Marotzke (1991) aad Marshall ad Schott (1999). 1a
the Maller stody,iCwas stressed that CA require uy nstontaueuus adjustoeul of te yates cola
while in ety the Eabe of sing tne i fle (of the order of 12h or so), Stated dilfsventl, the
CA adjustment scheme corresponds to an extremly large vertical diffusivity A. wheroas ove
epeets a

Ke Biha % hy @
Using w,—§ ums ond h 1 ke, ote obtains K, ~ 50 xis"! (Sead and Marshall 1995} Mar-
uke (1891) used &, - Lanta” while Klinger etal, (1996) used K.— (10 50) m?s-!, From the
o ese Carat sta # Oana Madi 7 (2008! 7 95
siewpoint of the vonsoquences of tbe CA sebeme, Bryan (L986) pointed cut that the standard
Ge Teb atheme leads n the collapse ofthe meridional crcilaion. On the otter hand, the olla
ivoided if one epploys a camplete mixing scheme ardior a trcatment of OC as # vertical
Jpfleion (Murotake, 1991). Revioning the problem, Pakisrkiewise snd Romen (1997) soncluded
hut the CA selemes do not produce realistic verlial density suvoture, do wot reate the eect
Jpuuntity of deep water, ancl da not wae a tame sate of adjuataaant in agreen-ent with tracer apes OF
Sigerestinas, Rm and Stomel (2001) bave peinled out. that CA viskls exeowive comvoelion that
Gpaalls tog much heat whieh Jn Lure yields Loo Ife sea ise cover, Finals, Yin and Saracik
(532) suggested and tested a sohene tat treats BC: wna vail difsion

“Te putt bp reassuring f a turhulenos model could reproduce the values of the veiticn! diffe
sivitice ned in theso heuristic odds, Ax we sill show tn Pg. 4, this is indoed the case

22, Turbadence morte

Ganspicnoesly absent the treatnent of deop eunvection kave heen turbulent models, as
pointed out by several authors. Kilworth ({988) has stated that “while model forthe ved
Bpnamie are legion, dione Cor doxp convection ate rare"; Maxworthy (1997) wrole that: “tus fa,
Seetunce schesacs huve tended ty be restricted to sueCace and local area modeling” apd thul “ous
Siznts to bape Uigt more complex closaresehomes wil be trod ou problems like deep convection”
wile Marshall and Schott (999) stale fst) “an effort should te mada to apply taem to these
Yeap comvoutve Dow’ nnd that “the challenge or the fut sto transfor the sighs sho-t
deep coureetion iaco a perarsctric epresentation”™

Fis paper b an atleopt to il is pap. Specifoally, we aueas the MY, KPP and G1SS motels
fon tha etme mining, Hateral advection is mudaled with che parameterization of Geat ana
MMewinieas (190), The dala on deep convection are fromt the Labrador Sea (Lavender ot ol
Sood), tm Ms present formulation, the GINS rod js local (aid jn ch final sages wf evo ution,
hed colnian in Fab {) and has no rotation, Thus, we expect that ¢he model will verestinate ha
atecctve depth ag the vealts presented below will iadeod show. In z econ study, we shull use
TeeetS$ local mod! (plus the GM model but with Une iueusion of ratacine in the vertical nixing
tae el hua thied study, we stall nclode nnr-ocaliy in tne GISS mrod! so as to nccous for both
‘foal ana dnal sages of deep cemvective prooesscs (lateral advection i still vealed with che GM
oieDy tt fousth study, 9 shall ws the GHSS mucdel employed in he third study, bul the
vrovce mode? will up Tonger bo the Gear McWilliam model but 9 now une (Camuly and
eee oe antmmtted for publication) that has boon developed und is presently being tested
agoinat data from an eddy resolving ocean vue

3. The GISS turbulenee model: general Feutares

“This vertical mixing model was consltncted using the Reynatds stress method (REM, Camulo
et alt 200le, 20ND, eted as C1.25 Cheng ot ul, 2002). 1 includes a velocity field und two active
Staley eld, temperature and safiity. The mudel ean be tine dspendont or sttfonusy. local ot
aaa al with oy witout rotation. Ip the sla dubary and focal euse, the ISS model des0mes an
ee Cane a Osan Madeng 7 BOCES 75-33 a

lgchraic at of equatious witose solution is analyice). The rect vertical mrbulut fs of
‘momentum, heat and salt are given by

ai

1, Taad S are the mean velocity, tempernture and salisiy. The vertical wy diltsiites
(ie stonds for momentum, heat and salinity) cap be written in two reprevenlutions

Ka —FeOE, Ka atl * as)

Ta 6s
ists miving lena nia the dispaton of rubutent kinetic energy, the ely turzovet
timo, W isthe Brunt-Vonala frequency, Zs tho mean shear aed ¢ a constant The sree
Foseiona 8, ae anal functions of thc Rihardson number A= 42/22 und of the ait alto
as /SfaDT oe)" where 2 aud fave te thermal expuncon und hata: euiracoo woe

ints. Orice the eu and salt diusves ao know, the panive soulur K- and ass diflasties
i, areabo known since

Ke BA REIUERD | Kea (Ry AKG) ‘43
“Te physical interpretation of ths model isa lls. ey the conention duc co win shear
eI eo tnerunl wa Hreaking fo convection fs preset. Soe es: processes ccs
Une lifsvity eis the sum of the te contibuions

Kaka +Ke (42)
Jn the ML, whore wind shen sh larger (ban the intorcal wave brcaking eomtribaton, the et
teem in (4) doncinates;bolow the ML, where wind skess becomes incPicene age Ri) she secon
teea in (de) dominates and thus « south transion of proccess is asmeed. When <0
{connective roping), the contribution toy by ineraal wae breaking hecomes negligible and Ka
15 pledeminaatly duc to convection

s(n ico}

4. Previous tests of the GISS model

Mixed layer and thermootie ‘he fist representation in (4b) vas used in C12 ancl by Burchard
and Holding (2001) aud Burchard ans Deleersn'der (2001). Below dhe mixed layer and i che
absense of deep convection, che mos! Rksly source of soixing is the breakiug of internal waves.
‘Using the second representation (4b), the value of adv # (42 > 0) de to insrnal waves breaking
seas taken fiom (Polzin, 1990).

Convective ofictecize 1, Since ther original iaroduction (Osborn and Cox, 1972), many
discussions have concentrated over the values of These couscotio effeioncies which, w'theut a
twebrlence model, remain adjustable parseceters, Several qcertans have remuined without ac
angst, For example: (0) are We Pye for pomeatem, feet and salt the same? (2) is ik comet 10
2 PMG Gat tc! Cate Madey? (258) 75 5

sestame Pag = 1/4 us ole dous, wea luge eddy simulation (LES) data (Wang ot ul, 1996) yield
the muett larger valoe Pz 1?

“The CHISS snodel couputes the F's which were shown to jnoreass vtrongly near Ry = 6, a
‘prodiction that is consistent with the raceat observations of a muck lngger mukxing at Barhados
{R= 0.6) than ar the NATRE location (Ledwell ot al, 998) where R, = 0,56, ‘The GIS model
‘alo predicts values of 4g np (© unity, im agrsement with LES data (Wang el al, 1936) thus
feasting daahis about the universality of the commonly used values 0.2-0.28,

"NATAD data, &q have often been assured ta be the seme bat the NATRE measnzements bave
sttown that Ky 9f Ke Several anthers have investigated ho iaflconcs of double dilusive processes
BL OGOMs (Zhang etal , 194% Merryteld et aL, 1999), Some authors weated the ratio Xy/K, as
free parameter, allies (Large ct al, 1994) exwpluyed ths relation K, — 143K {however the
incastremtents shave hat & = L43Kii!), Tn general, these stusicssoncluse ikat double difasien
alters substentally he eegional dlswiaition of 7 unal Saul dhat salt ingers are more widespread
tan diffsive convection. Compared nith tke Kj =X, case, deep temperature and salinity become
large, the polar heat trnnspart is fowered and the meridional uverlemning is reduced, Given the
Ineupstc nature of Lae clatfon Kes employed Unis fa, it is ffl! ta woeapare andor asses the
reliability of the ensuine results,

Tests without ax OCCA. Since mt 400 m depth ike difusvitioe are only functioas of Ry the
valsos of 2y(2) meanuted at the NATRE site (Lecwoll ot ab, 1998) were used to compte the
Coneenlration auxl mass diffvsviies from Eq, 4d). Comparisan af the CISS medal results will
the NATRE date was provenled in Fig. 9 of C2. Unpublished results trom data ut Barbados
(RAW. Schunite, Mawaii Queue Scienors Metin, Meh. 3002) of a mu larger mixing at Barbados
haa ne NATRG, are alse in qualitative agreement with tbe predicsions of the anadel

“Tere with an OGCM, The GSS model was us0d ina coarse rexolution OFDL-ype ascan code
and the heat sat, mast and concenttation difhsivties at the NATRE location were vempuled
‘and sloyta to reproduce the NATRE data quite clowely. The 7S profiles im diffrent ucean’s sites
‘ware alen eampaled 2nd in general they roprialuce the Levirus dats well. Partiulacy signiteaat is
the betta agreeraent of the T vs, x profile in the Arctic Ocenn

5. Modeling deep convection

5h, 33" resoion

‘We have employed the NCAR-CSM global gccan model (Large at al, 1997; for delay see
Appendix A with 33° revolution, The model requiresa vertical micing achemne and employs
‘GDI model to paraatsterize che mesnacate edlies, We ran ton global simulations with 190 dit
vent vertical nizing sebemes, the KTP modo (Large etal, 994) and the GISS model discussed
above, Tus monty eurace forcing calculation and alt her aspects ofthe two OGCM run eve
Sdktial, To compare the model results with abservations. in Fig, 1 we reproduce the reslts of
Lavender etal. (2002). Measnrements show ubut the deepest comnretion, DC, we with mixod-
layers decper than 08 hin is emvfived to the Laily sull Tavonder, Davis aud Owens (LO)
sesion in the westera Labrador Sea, Fg. J. A simular rut presente ia Fig, 12 of Pickart ot al
{2002}. Tn Figs. 2 end 3, we exhibit the GISS ang RPP simulation points found to yield deepest
VM, Ca ta # Owns Moding 7 20041 75-95: 8

aiw sw cw <sW cow
ip F Wine er del a fou Laven ot a 002)

ig. 2, DC Gin fn he SS ing nd

convection (the rests are svapshos Calen ut Mirek 1 ofthe 127th year), The GISS xing model
reproduces the deepest sonvsetion in the LDO region while the KIPP modal docs not, Within the
EDO regio, the KPP rcined layers ace not deeper than 7m. Deep comvection inthe GTSS model
js evident in both the fut verLval tempecature protile anc large Usot diflusivity down ty 1.2 Kaa
Fig. 4). The GSS model heat dfusvigy in thes eolimm increases fram 0.04 os " wear the
jsufaee toa maximum of 6x25"! at Um, In ether colueans, we find maximo diffusivities up 10