ocean circulation and global climate change

Chapter I

Ocean Circulation and Global Climate Change

Kxemtive Summary

PrQMp$0 artd OppOFtQpffty Research Strategy

' . For several years concern has been mounting thatthe earth's global environment may be changing inways, to which we can not easily adj ust. The long-termtrend in atmospheric carbon dioxide and the knownradiative etects of this and other trace gases, and recentdata suggesting signigmnt changes in the ear th's ozone

. layer are evidence of fhe potential for major changes inNe global climate.

, 3t is clear that man is no longer a passive participanti' the global environment, Human activity has reached

' &' scale rvhere it affects fhe global environment in.tuep that wedo not fully. understand. The effects of thisactivity, coupled with the natural variability in thePobal climate system, anil have profound implicationsfor the future. Current and anticipated changes in theglobal environment will produce significant economic,social and pohtical problems which this Nation, incooperation with ofM rtations, must be prepared toaddress:

'. NOAA has the respotisibility to understand and ul-'. - 6'ttmtdy fvrecast interartnual, decadal and longer term, doute change, Qn,these time scales, the transport,

' .ifq%gemd exChany'' 'of heat by the surface'and sub-mrPbe waters of t4' viorld oceans, and the mass, mo-

tum and energy excludes between the oceans and't4', atmosphere, are'of crucial importance in influenc-

, . utgdbnate chdnge, ',,

The climate system can be characterized as a globalheat engine having two working fluids ' the oceans andatmosphere! that transports heat mainly from the equa-torial/tropical zone to the polar regions. The research .goal is to be able to understand and predict the behavior. ch'mate! of the system on different time scales.

The research strategy is directed at resolving thecritical questions that must be answered in order toachieve the goal. First, the behavior ef the system thatneeds to be understood is defined from current observa-tions and reconstruction's of its past behavior. Then,understanding is, derived from diagnostic studies of theobservations and through numerical simulations of the .response of the coupled atmosphere and oceans'. An-swers to critical queshons provided by focused researchserve to refine both understanding of the system and .the simulation models. Refined modhls ultimately'pe-,,vide the basis for predictions of the future be~or gthe system.

Three broad tasks must be agdremd. These are;:ocean circulation models must be refined and verified;observational systems must be designed and deployed .for ocean climate mvnitoring; ad nero in situ technol-', 'ogy for ocean mo~itori~g must bj devejoped.

The top level questions about the global heat, eny'nethat need to be ansmredare: ' ~: ' ',

+ what is the heat transit, of the oceans fkow '.much aml from where o where!~

+ how is the transport performed rvhat rvater raasseA,are involved and how is the system. forced! P

6 Ocean Circulation and Global Climate Change

Why Now?~ what is the temporal and spatial variabihty of thebehavior?

~ hozc> do changing ocean conditions influence theatiiiosplcere and zohat creen» features are most im-portant in fhis respecf?

These qccestio»s lead fo increasingly i»ore specificqicestion» which the research strategy must address.

A specific research question of importance ininteranriical climate vaiiability concerns the»ff<'ct o»the phenom»cia associated with El Ni»o a>tel th» Soutli-ern Oscilafion EXSO! of zvater mass exchanges befzci»enthe Indian and Pacific Ocea»s. On interdecadal andlonger tinie scales, some importarit research clic»sfionsconcern:

~ the role of North Atlantic deep uiatei formafioii,ana' exchang»s u>ith the northern brariches of fhcsicbfropical gyre, iii regulating the therniolialinecirculation, acid

~ the identification cif feedback control ineclianismsin the Atlantic. ther>nohaline circulafio» and theirrole in possible major, and relatively sicddeii, cli-niate changes taking place c>n tlie ccczt<cr<f tiinescale.

On bofh iriterannual and inferdecadal time scales,some important res~arch cluestions relate tc>:

~ understaiiding the dynamics of the oceacz/atmosphere fluxes of heat, inoistuie acid inomen-tuni, particularly u>itic respect fo areas co><trollingthe tin« -variability of zziafer rriass formation,

~ the relationship of changes of heaf co»te»f of theecluatorial .ones and changes in the position of theIntertropical Coiivergence Zone ITCZ! and theirrelationship to climate variabilify it> higher lati-tude», particularly in the Atlantic basi».

7lic uiorld oceans play a central role iii el<i»atecha»ge, and th» probl»ms pres»nf»d by global climatechaiig» aii very real. Recent scientific advances andpl a>i neil technological i in prov»ments e.g., sic per-coinputers and safellit» systems! now >nake it possibleto fake a truly global look at fhe earth, inclicdiiig theuiorld oceaiis, as a systeiri and engage, for fh» first time,iii a riatioiial and internatiorial! scie>itific program toii»derstand and pre<fief changes both iiatural and rnaii-iiuide! iii fh» global »nz'iro»ment.

Benefits

Tl«' earth may face' climate and eiivirorini»«talclianges oii tiine scale~ of importance to living genera-tioiis, their civilizafions, arid fziture progeny. Tliesechanges rriciy be dice to natural z>ariability, or rica>/ behi<via>i-iiiduced, such as fhe effects of inc>easing CO,levels a»c4 changes iii ozone levels. Regardless of thesoiirce of change, the ability of scieritists to predict thedirection acid iiiagnitude of change u'ill allozv nationsacid inter»atio«al institutions to be better prepared to<ice<>»inioclate to these changes, or to otherwise mitigatetheir coczse<7u»>tees, 7'he research strategy laid c ut foroceaii circiilation is clirecfed toward proz>idi»g fore-casters a>id modelers zc;ith refined ocean models haziirigI>re clic tizic' cat>abilit<f commeiisurate zoith the E'xistingatniospheric inodcls a>id to support devek>pin»nt ofco«plea' «iodels of the fuio fluid systems.

properls pose tlie sequence <if questions th,it needst» be at>su ered,

l« their last cciiniersatioii, Alii c H. 7'oklas czsk»c$ ..< r-fr<cdc Steiii, "1%7>af are fhe aiisucr., G<'rti»?" C<cfcccd»Shit<'s reply zvas, "Hist, <vhat are thc' <licestioiis, Alici?"

Research is dire«ted toiyard a goal, most oftenposed in tcrni» <if a question, or questions, to beanswered. In particular, there is usually a logicalsequence, or hierarchal order, of questions leading tothe goal or purpose. The most general question at thetop of the hierarchy must set the proper direction fora research strategy designed to achiei.e the goal.Therefore, the first order of business in formulating iivell focused ocean clim;ite research strategy is to

Tlie traditi<in,il detinition of climate is the long-terin beli,iyi<ir ot the itniosphere, described in terins<it, iyerage» of the bisic parameters thit charicterizethe iyeatlier, such as temperature, pressure, vyindi elo~iti, and precipitation. C.limite is then distini tin>m th» climite system, vyhich consists of those ele-inents ot the earth system that determine «limat<.

These are, at a minimum, the total atmosphere, theoceans, the land surface and the cryosphere Fig-ure 1!. If our ultimate goal is prediction on climatetime scales, then we must concern ourselves withsimulating and predicting the interactive processesof the climate system.

The essential nature of the climate system illus-trated in Figure 1 is a "global heat engine" involvingtwo principal working fluids, the atmosphere andoceans. The oceans and the atmosphere redistributeheat between the "sources" and the "sinks." Themajor source areas are located mainly in the equa-torial and tropical regions, while the major sinks arelocated principally in polar areas. This description of

the climate system provides a self-consistent meta-phor for formulating critical questions and a researchstrategy to answer them. In order to predict changesin climate, we need to answer the question:

~ What is the temporal and spatial variability ofthe forcing fields driving the two working fluidsof the global heat engine and what is the vari-ability of the response of these fluids in spaceand time?

This constitutes the most general question whichthe research strategy must address.

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The ultirnatc driving force» of the climate svstcm'shc«t engine «rc the inc<>ming solar ridiation, theoutivard radiation fliix thc reflected «lbeiio field

and planetary radiation!, the gravitational and rota-tional Corioli»! forces. In terms of the <icean», themain fields associated with the torcing ot' oceaniccomponent ot the heat engine act at the interfacebetween the <>cein»;md thc atmosphere. These fieldsare the distribution of wind stre»scs, thc fluxc» otsensible aiid latent Iicat, and mas» fluxe». Thc m,issand latent heat flux< s are mainly concirncd ivithmoisture transp<>rt at the ocean surface. The heat fluxalso i» closelv related to sea surt'ace temper iturc SST!distributions. The main fields associated with thc

forcing of the a tmosphcrc are the sanie»urf;icc fluxe»ind SST field, but the corresponding quantities forthe Iand arid cryosphere surfaces also arc involved indriving the atr<iospheri«circulatioii, Hence, definingand understanding the spatial «nd temp<>ral vari-ability of these ocean surface fields must be an im-portant concern of the research strategv.

Starting with the general question above, a logi«,ilsequence ofque»tions for ocean climate research fol-loivs with:

~ What qua ntitv ot heat is transported bv the globalocean» and how is that transport distributedgloba llv?

~ How are the diff«rent oceanic water masses in-

volved in the specifics of the global heat trins-port?

~ What is the temporal variability of the oceanicheat tran»port?

At the same level of generality, thc next que»ti<>nsrelate the role <if the <iceans back to the atmosphcri inthe overall ghobal heat transport problem:

~ How do i.hange» in the oc«anic heat transportintluence the «tmosphere?

~ What arc thc most influential features of the

oceanic heat transport svstem affecting the atmo-spheric v;iriability?

Sequences iif incrcasinglv specific questions fol-low from thc above, and these are posed in thc sub»«-quent sections.

In <>rder to predict climate change, wc must dealwith the complexity of the earth as a system, where»ignificant. ch«nges may take place graduallv over<'cnturies or relativclv dramaticallv over a time pe-riod encompa»sing the lives of a few human gcn<.ra-tion». We can not afford to wait whilcwe «ccumulatc

adequate time series of basic geophysical variables,nor can we aft'ord to undertake what inadvertentIv

might become irreversible in sit<< "experiments" onthe cliniate sy»tern itself.

C<in»cqucntlv, cv< n more»o than ivith the ive<itherprcdi«tioi> problem, ive must depend to a gre«t ex-tent <iii devel<>pment of sophisticated < omputirm<iiicl» tli,it cari be used to perform vari<>u» numcri-« i1 experiment» hvpothcsis testing, »en»it..viti analv-»i», »imulation, di«gno»i» and predictions!. Dat i oiiflic p i»t bell«i'ior of the climate»ysteni ivill,iI»o heni i.c»sarv. Back bcvond about two ccnturic» in time,

thc»c dat,i must be derived from indirect »ourcc» of

inf<>rin ition, such as lake levels and ice core>. The»erc«on»trii<.tcd time»eries wiII serve to define thc

bch«vi<ir that ivc seek to understand, Thc retro»pe«-tii « d ita ivill be used, al«liig with current <i«ta froniiiioliitoring sv»tcms, in thc model development veri-fi««ti<>n, «ilibr«tion, and assimiLation! aiid,ippIic i-tioiis »imulations and predictions! portion» <>t thcKOAA pnigram. I nderstanding gained from ivcII-forniui«t«d rc»circh efforts int<> thc fund,imental

<iie ini«pro«c»»c» <ind «ir«ulation p<ittem» ii ill »cri'cto,>dvan< e the iievclopment of the circulati<in mo<i-el». Di,>gnostic effort» md simul«tions u»ing theadvanced niodels provid< more snphistica'':ed in»ight»i»t<i tiie «limatc»v»tern, refine the researcIi q iestions<ind»o forth Figure 2!.

Calibr,ited .ind verified model» that c«n explaintlie p,i»t behavior of the climate»v»tern, including"glob«I «limatc changes" in prehistoric and even hi»-toiii tinic» e.g., thc Little Ice Agc! ivill iventuallypnividc the basi» for reliable predictions ani1«s»cs»-ment» ot tuture changes in the worM's cliriiate»v»-t<. ni. An c,irlv step in the process ivill inv oii c,ipplic,ition of »urfa«e <vind stress fields re«onstru«tcd from

about,i «cntury of liistoric observations t<>»imul,itcth» global ocean circulation. The corrc»p<inding hi»-t<iri«re«<ird of SST Sea Surf««c Temperatur<>! ob»cr-x ition», in«Iuding the po»it<on of oceanic front», willb» used al<ing wit li the sparser records <>t land-ba»i d<>b»eri,itions to»imuI«tc the past circuI«tion patternsof thi atni<i»phere, Limited historical record» of sub-»urf««c o«caii <>b»ervations are availabl» foi valid i-

ti<in.

On «lirnate time seal«s, rn<>»t of the true ixternalf<ir«ing 1'unctions are now variable: they must beexpliiitlv dealt ivith in the prediction problem. Also,tiic i«nil, ocean and cryosphere are fuIIy «<iupIcd tothc,itmo»phere in both «dynamic mechanical cn-crgv! «nd thcrmodvnaniic thermal energv!»ense Figurc I!. If we look at the climate prcdicti<>n prob-lem !n>m the side of the atmosphere, ivhat had beenes»cnti,illv I'ixed ocean, land and crvo»pbere bound-ari «<>ndition» for the weather prediction problembe«omc time-vari<iblc as we address the longer cli-mate time scales. I-'or example, the sea»urf,ici' tcm-

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NUMERICAL CLIMATE MODEL SIMULATIONAND PREDICTION

Figure 2: Application of Ocean Circulation Models and Ocean Data inClimate Simulation and Prediction. Ot ean data mrculation, thermo-dynamic state, surface fttnes! provide a! initial!boundary values forocean c rcuiation models coupled with atmosphere General CirculationModels GCMsr and tnodels for cryospheric and terrestrial inter-actions, b! identification and removal of systematic errors in historicaldata for use in the climate model calibration and veriftcation process,and as statistical constraints in data assimilation mode! for c! simulations and d! predictions of climate changes,

peratures shift, significantly with the seasons, as doesthe land surface albedo and sea ice extent.

On time scales beyond the seasonal, the dissipa-tive processes cause the atmosphere to "lose mem-ory" of the initial conditions, so that the boundaryconditions dominate the behavior of the atmosphereon long time-scales. However, the natural responsetimes of the oceans, cryosphere and solid land aremuch longer than those of the atmosphere. Conse-quently, while the atmospheric side of the climatesystem is dominated by boundary conditions on cli-mate time scales, the initial conditions for the oceansand cryosphere will still play a major role in theprediction problem for the total climate system.Hence, observations of the present state of the oceansare essential for model initialization.

Oceanic relationships to the boundary conditiondominated features of the atmospheric system arecertainly candidates for focused research. Experiencewith the GARP Global Atmospheric Research Pro-gram! and GATE GARP Atlantic Tropical Experi-

ment! programs brought early recognition that a cli-rnate program would need to focus on numericalmodeling as a basic means, and prediction of climatechange on different time scales as a basic end. Fur-thermore, the understanding of the roles of the oceans'transport of momentum and heat including inter-actions with the cryosphere! were seen as being deci-sive for the development and application of climatemodels. In the seminal GARP document Doos, et al,,1975!, it was emphasized: "On seasonal, annual anddecadal time scales, climate models must take intoaccount an interactive upper ocean and sea ice... Onlong time scales e.g,, 100 to 1000 years!, considera-tion must be given also to changes in the deep oceanand the variations of the continental ice sheets... Therole of the oceans is believed to be a dominant one onclimatic time scales."

Two decades ago, E. Lorenz �968! speculated thatthe large scale behavior of the climate system mayexhibit nonlinear instability under certain circum-stances, particularly for its long term behavior. Evi-dence for this kind of behavior in the global climatesystem is the apparent abruptness of the onset of atleast three major cooling episodes or glaciations overthe last 150,000 years. The evidence suggests that asubstantial portion of the cooling effect may havebeen experienced within the interval of about a cen-tury Lamb, 1982!. There also is evidence that lessdramatic examples of sudden transitions in the cli-mate system have taken place within the last 150years. Fletcher et al. �979 a,b! noticed sudden dropsin the strength of the Southern hemisphere Wester-lies in 1870, 1903 and 1917.

The conventional concept for climate change seeslong-term change taking place continuously andgradually as a quasi-linear process. Many adherentsof the greenhouse warming hypothesis accept thisconcept implicitly and expect change to take place asa gradual, more or less irreversible trend, The evi-dence for a gradual global warming since the begin-ning of the industrial revolution in the mid-eighteenthcentury is usually taken to support this gradualisticconcept of climate change.

However, Broecker �987 a, b! has presented achallenge to this conventional view of climate change.He points out the evidence for a number of veryrapid transitions, mostly from and occasionally to,cold periods including full blown lce Ages! and

~ ~

cites evidence that dramatic changes in atmosphericcarbon dioxide content may have been involved insuch climate changes. He also concludes that theevidence suggests a key role for some mechanism inthe North Atlantic involving a shut-down of theAtlantic portion of the density/salinity-driven deepcirculation thermohaline circulation, Figure 3! trans-porting the excess cold waters of the Atlantic into thePacific. Recently, Manabe and Stouffer �988! havedemonstrated numerically, using a coupled ocean-atmosphere simulation model, the existence of a bi-stable equilibrium condition for the climate system,at least within the approximations and limitations ofthe model.

Such a bistable state involves two modes of the

climate heat engine having markedly different statis-tical averages of the principal variables i.e., climate!.Each mode is stable for a wide range of boundaryvalues and forcing conditions, but both states aresimultaneously possible for a relatively narrow rangeof the boundary and forcing conditions. The climatesystem can make relatively ra pid transitions betweenthe two modes of the bistable state, under the condi-tions where both modes can exist. The climate sys-tem is actually unstable for that narrow range of con-ditions and markedly increased variability over arange of frequencies can be expected.

Basic observations concerning the role of thethermohaline circulation in long-term climate changesuggest that high latitudes are regions of critical pro-cesses including ice processes! and that salinitychanges are critical, if not decisive, for the operation or shut-down! of the thermohaline circulation sys-tem Bryan ef al., 1988!. Hence, changes in salinity along with temperature! are the key observablesthat must be mapped and monitored. Other impor-tant observables are related to surface fluxes, inter-actions with major wind fields, and sea ice inter-actions.

The field of global sea surface temperatures isgenerally recognized as a key climatological vari-able, as it is the major boundary condition related tothe forcing of the atmospheric circulation that is alsoreflective of ocean processes, Analyses of the avail-

hear~ 3: 'Ihc Great C?cean Conveyor Belt <Broeker, 1987hz A. oripltfiet r.*ion of the thcrmohaline ctrcnlatioa sVcte~n of the elohalo ceo o +

,able SST record» see for example F<>11<and»t <>t., 19S >,and I'arker, ]9871 identifv three prnminc>at raa<ade» ottemporal variabilitv, other than thc annual sign,il,These are: <lri interannual signal rcpre»ent,atii c of theEI Uino related phenomena and having,i mainlvtropical ocean focus, a signa? reflecting intcrdecadalfluctuations, and 1 long term warming trend. It i»temptilag tn identifv the long ter>aa trclid 1» being <92sccul<ar c?>a>age duc to greenhouse iv<arming, but gii'enthe limit«d duration of the available record it canonlv be < haracterizcd as represent,itive ot ccnturvscale or longer fluctuations.

The stroiage»t, most coherent, int«riniau<al clilrla't»signal» knoivii arc in the Equatorial Pacific and arccategoriz d,i» ENSO El-Nino-Southern Oscillation!phenomena. The ENSO manifestatiiins inchide: thcsee-s<aw oscillation Southern Oscill<atinn! in atmo-

spheric prcssure as recorded in Darivin, Au»tralia iiithe Iii<'est, and Taliiti in the Eastern Equat<>rial I'acific;El Nino, tlie strong thermal anomali in the Ea»ternTropical Pacific, off the Peruvian,ind Fcuad<irianCoasts; and the general pattern of tropical Pacifictemperature and sca level anomalies,and prop;iga-tion of trans-Pacific Kelvin and Rossbv ivave». Th«rcseems tn be some degree nf corrcspnndencc in theEquatorial Atlantic, but whatever signal cxi»t» theredocs not »eena to be as strong or c<iher< nt. An ex-ample of,a relatively pronounced intcrannu,al »ignalin the Equatorial Atlantic i» the upivelling in thc Gultof Guinea in the Eastern Tropical Atl antic.

The clinaatcs of the major land area» <it thc Pacificbasin Australia, New Zealand, Coa»tal China, ['cru,and California! also tend to shnv< a strong inter-annual signal a» the dominant effect it cliria«tc fre-quencies h>wer than the»easonal/annual band, Gen-erally, thc interannual signal in the I';icific tends tobecome iveaker and less coherent at higher latitudes,but remains pronounced neverthc lc»s,

In the Atlantic, the signal strength and cohere>iceof the interannu<al sign<al are also diminished <as icenaovc aw iy from the Equator, and diniinishcd over-all conapared to thc Pacific manifc»tations. In theNorthern Atlantic, the intcrannu,al oscillatinii fre-quently is n<>t as pronounced a» thc dccadal/interdecadal climate»ignals Cavan, 19871.

The dccadal/intcrdecadal »ignal »h<>ivs almn»t,anopposite character from thc intcr<iii»u,i I sign.il ivithrespect to its geographic distribution. G»nerallv, thc

r< I,i tii c»trength of the interdecad<il sip«al is strongerin th» AtI antic Ocean and Atlantic b,a»in land,ar«a»

than rt i» in the I';acific, at least outside i>f thc Tropic» C, >i an, 19871. The most prominent interdecada1 cli-mate signals relate to the Saharan/Sahel dr<aught inN<irth Atrica, and thc Mid-N'e»terra dr<iught «i clc ntth» united States, ivhilc the drought v;at tern in North-«a»t«rn Brazil near the equator does not exhibit arelative pronainence of the interdecad;il componentiit thE signal over thc interanniial Lamb <'t <rt., 198 >1.The rel,ativ«strength of the interdccad.il cliii«itc sig-n,il compared to tlac interannual nscill,ations tend» toincri a»»,as ive move North and South aiv,iv from thcI-:<]uat<ar in Iioth ocean».

Tlic relative strength» of thc interannual and><at»rdcc idal climate signal» over the gl<>bc can be de-siribed,is;i str<inger intcrannual effect mnduIatcd1>i' a ivcaker intcrdecadal sign al for thc Tropical Va-iitii basin <a» a ivholc. To s<>me degree this holds truetnr the Equ,itori<al Atlantic. A»trongcr interdecad,al»ign il m<id u lated bv <1 i<veakcr interannu<il cffe< t tendsto bc m<ire «haracteri»tic in the higher I,ititude».

<a. p<i»sible sequericc of gl<ibal ocean circul,itii>npi»>grani», prioritized as to allncati<>n of rcs<iurce»,<ind de»igned tn naakc r<ipid progress in understand-in«' it cliuiatc change on thc interaniiual throughinterd«cad,al/century time scale», r.aight start withthc interannual »ignal. It ino»tlv ini oli'cs tlae <icean»urt'ac», atmo»pherc and some major surface current»v»tern». 'Yea»urement» in thc loiver atnin»ph«re and<vitliln t lac nce<111 surface layer» arc the most cn»t«ffcitiie. Thc Equ<atoriai Pacific, ar ith the best d»-tin»d .a>id localized cffcct» nf this kind< iv~>uld,ippearto bc the b»st place t<> start, sub»equentlv m<>vi»goutward to the Tropics, then the middle latitudes inthc I'acific <>r the Equatorial Atlanti<i I hc neighbor-ing Ini]ian Ocean, iihich behaves simpathcticallvivith the Equatorial Pacific, ivould also r»ceii e earlyatt«ntion. The Atlantic equatorial and tropical zone»could f<illoii next if riot given attenf ion. earlier, andhigh«r I atitude areas of the Pacific a>ad Atlantic wouldprnbablv bc Last.

At »omc p<>int, thc studi'of thc interdi'c<adal »ignal,ini1 th«d«cpcr <icean, with the greater a»»ociat«di o»t»;ind teclinic il dift icultics, iv<>u1d gct underiva v.Ag«iii, th» best place to st<art would al»n be ii h»rc theinti rd»cadal signal trend» to bc cle,ire»> and str<ang-«»t <ind that ivould be in thi North Atl,intic, pnibiblv

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PROGRAM START-UP DATES Year!

following to the South Atlantic, the South and NorthPacific.

This broad strategic approach to programmaticprioritization and sequencing is, in essence, whatNOAA has been following since the inception of theOACIS Ocean-Atmosphere Climate InteractionStudy! program in 1984, and in certain respects forthe last ten years since about 1979. OACIS, whichwas the predecessor of the TOGA Tropical Oceanand Global Atmosphere! Program, and TOGA itself,set the strategy firmly in the mode described, for theinterannual process by 1985 Figure 4!. The STACS Subtropical Atlantic Climate Studies! Program setthe pattern for the decadal problem with its Atlanticemphasis in 1982.

The prioritization described above would be flex-ible. Certain investigations might be conducted ingeographical areas out of the suggested sequence.Any critical features of the ocean surface fields in-volved in the forcing of the global climate heat en-gine would be candidates for special priority. Ex-amples include regions of high wind stress in theSouthern Indian and South Atlantic Oceans, the Ant-arctic Convergence Zone and major oceanic fronts inthe North Western Atlantic and North Western Pa-

cific Oceans.

Figure 4 Evolution of NOAA Ocean Climate Programs. A summaryview of NOAA OAR ocean climate programs since 1973 witli meteoro-logical antecedents since 1963, and projected programmatic strategythrough the first decade after the year 2000,

The programmatic basis of the NOAA researchstrategy in ocean-climate, as articulated in the 1979plan Fletcher, et al., 1979!, led to a series of budget-ary initiatives for specific program elements over thenext few years. Out of this planning and budgetaryprocess, emerged four new core programs see Fig-ure 4! which were to form the foundation of theNOAA programmatic strategy in ocean-climate re-search for the next decade.

All four core programs have supported the devel-opment of basic means technology and techniques!required to conduct subsequent programs. All ex-cept the Comprehensive Ocean-Atmosphere Data Set COADS! effort, have focused upon specific regionalproblems and basic processes that are representativeof important aspects of the general ocean-climatesystem critical to the development of understandingof climate change. COADS is fundamentally globalin concept and approach, but with regional resolu-tion. Together, the four programs cover the entirefrequency band in the climate system identified asthe concern of NOAA's long-term effort seasonsthrough centuries! and represent the essential firststeps toward realizing the overall predictive goals.

Ocean System Studies I 13

<>t NOAA's chemical tricer work in the mid- 1980's.

The «hloroflourocarbon tracer studies hid the addi-ti<>n il ad vant ige of being complementarv with otherglobal chemistry and carbon dioxide flux work sup-porting NOAA's ocean climatic mission, i.c., the<>cein'» role in the greenhou»e problem. Th< workli 1» progres»cd <it rting otlierNOAA clim,ite research progranis.

A thircl eftort, Transient Tracers in thc Oceans TTO!, ha. been intcrmittentlv funded a» an internal

effort supporting other programs, and has been di-rected at a sequence of regional problenis havingmuch broader implicitions for climate. The 1979NOAA strategy docunient noted that plans ivereunderway for one study, "Transient Tracers in thcOcean," using "radio-carbon and tritium tracer»," tostudy "re»idcnce times, transport mechanics,indvertical n<ixing." However, under the subsc'quentbudgetarv constraints, the fritium work iva» judgedto be too expensive for NOAA's limited resources, »othat clilon>f'Iourocarbons freon»! bccanie the focus

A tifth sct of programmatic efforts not identifiedin I'igure 4 started earlier than the oth»rs, and willassume grov< ing importance in the future. Thi» is the<>ce i n circulation/climate dynaniics modeling devel-opment» th;it have been ongoing as bise efforts intli» Gcophvsical Fluid Dvnamics Laboratory .FDI.!»inc» the mid 196 ys. These model devel<>pments andnunicricil experiments also cover the entire «Iimatefrequency band of concern. Like COADS, they do notinc oli e field work, but <ire invoh ed in developmentof e»»»ntial techniques needed to achieie th» ulti-rn«tc predictive goal» of thc program.

Two <>f the core prograni», Equ,itorial PiciticOcean-Cliniate Studies EPOCS! and STACS, are theeirliest and are officiallv funded a» ongoing baseprograms t<> this dav. In 197S/79, NOAA initi<itedthe EPOC'S program to study the cause» ot the largescale sea surface anomalies in the equatorial Pacificand their effects on the atniosphere. Thc Equatorialand Tropical SST distribution is believed to be a1n <loi f<lctor in the forcing of the atmospheric conlpo-nent of the global climate heat engine. Because of thelarge intcrannual signal in sea»urfacc temperature inthe eastern equatorial Pacific, initial studies were di-rected at this region.

Oceanic heat flux is generally believed to be animportan process involved in intcrdccid<il cliniatevariabiliti. However, long-term m<>nitoring of thesub-surface <>cean processes on interdecad il timescales pre. ents a forrnidablc challenge. In 1982, NOAAbegan the STACS program hir studving the tr insp<irtof equatorial heat to higher latitude» in the Atlanticand related processes. The initial enipha»is of STACSwas directed at the western boundarv currents of thcNorth At.'.antic Subtropical Gyre, in particular, theFlorida Current «nd Gulf Stream, ivhich have beenshoivn to be a major component in the ivind-drivenniodes of Atlantic heat flux and the subtropical gvrc,Given the int»rdecadal and interannual implicationsof the program, it is shoivn in Figure -I <is based up<>nboth of th 'sc frequency band».

Thc fourth effort, the Comprehensive Ocean-Atmosphcre Data Sct COADS!, is ilso internallyfunded and has continued at a steadv low I»vel of»tfort tor nearlv a decade, but unlik» the <>ther tlircc,docs not involve an actual field >neasurcment pro-grim. GOADS represents a systcmitic attempt to u»ep,i»t dat4, ships of manvcountries have been taking regular ob»crvati<>ns of1<>cal <vcather, sea surface tempcratur», and nianvother chat,icteristics near the boundarv betiveen theoc»,in and the atmosphere. In liter vears, fixed re-»ea rch i c»»el», buoys and other devices have contrib-uted similar marine reports. The collection of surfacedata»pinning the global oceans, from the mid-nincteenth century to date, is the hi»t<>ricil ocean-atmo»phere record utilized in the COADS effort, To-gether, these four programs forni the four leg» uponwliich th» NOAA ocean-climate»tr«tegv stands.

Since the inception of EPOCS in 1978, NOAA'socean-climate research strategy for interannual timescales has been executed through a sequence of »pe-cific programs: EI'OCS, OACIS, and TO A see Fig-ure 4!, EI'OCS concentrated on the equatorial oceanbetween about 20 degrees N and 10 degrees S lati-tude, with th» major initial emphasis on the domi-nant equatorial I'acific Ocean phenomena, In 1983,starting with the EPOCS scientific plan, the NationalAcademy of Sciences NAS! produced a national plantor a program called OACIS that was directed to-ward the problem of interannual climate variability.NOAA initiated its part of OACIS in 1984, building>round the continuing EPOCS effort. When the WorldClimate Research Program WCRP! adopted the»trat-egv of OACIS, it was developed as a full interna-tional program called TOGA. In 1985, NOAA sub-sumed the EPOCS and OACIS effort» under the

international program plan see Figure 4!.

The program title, TOGA, defines the essence ofthe main concern: the role of the dominant inter-

annual processes of the tropical ocean and itsinteractions with the global atmosphere producinginterannual climate variability.

After extensive review and debate, the TOGAProgram proceeded with the broad strategic conceptoutlined in Section 2.0, continuing to concentrateresources allocated to investigations in the interannualclimate research area, first for investigations ot lowlatitude I'acific Ocean processes, then moving out->vard to higher latitudes Tropics and Subtr<>pic»! inthe Pacific, the Indian Ocean, then the tr<>pical Atlan-tic, etc.

During the initial implementation stage of TOGA,the major cor>cern was the strong equatorial Pacificwarmings which occur at irregular intervals of about2-7 years. However, now both diagnostic studie» andtheoretical work have more clearly delineated th»global tropical linkages associated with ENSO vari-abilitv, Recent work also indicates an important roleof the large-amplitude, coherent atmo»pheric fluc-tuations on the intraseasonal timescale '30-60 dav

>vaves!. As a result, the current description andunderstanding of tropical ocean-atmo»phere variabil-

itv involi es a br<>adened focus for TOGA to i~eludethe, >s vet p<>orlv understood, "global teleconnec-tion»," relating global interannual oceanic and atmo-»pheric phenomena, The full ENSOcycle, rather thanjust the >~ arm episodes, and the intraseas<>nal modeotvariability also are included in the nerv focus.

The limits of the tropics, bv usual definition, areconfined bv the + 30 degrees latitude band, >vhichace<>unt» for about one half of the Earth's»urf«ce.

However, as a practical matter the ocean concerns ofTOGA arc approximatelv bounded by the < -I0 de-gree» latitude band, providing a beginning to exten-»ion of the monitoring system into the mid-latitude».The exten»ion of the monitoring svstem i» es»entialfor understanding the nature of the teleconnecti<>n».

The m >ssive I'acific warm epi»<>de of I 982-83 wa»,>»»ociated with a clearlv defined pattern of inter-ocean teleconncctions around the equatorial belt.The»e ei olved over a period of about three vear» toinclud<a»trong and >veil defined global signal inrainfall, atmo»pheric circulation and SST. New analv-»e» of the hi»torical data have shown thi» to be a

recurrent mode <>f interannual global variabilitv inthe tropical o«ean and atmosphere.

The tropical Atlantic also ha» a mode of inter-;>nnual variability that has many similaritie» >vith theI'acific Ocean manifestation of ENSO. The tropicalAtlantic mea»urement program under TOGA duringth< next »e>. eral vears aims at providing data to checkthe hvpothesi» that change» in the position ot theIntertropical Convergence Zone ITCZ! relate to«hange» in the h< at c<>ntent of the equatorial x<>ne.'Ihe»e effort», which will probablv extend bevondthe I' !GA time-line, are also candidate» fc>r TO Ainteractions >vith the World Ocean Circul,>tion I'.x-

periment WOCE! Core 3 I'roject that i. c<>ncernedwith ocean gvre dvnamic»,

Th<. I 990'» will be a period of intense interagencvand >nternational research in the oceans, in~ <riving atle>st tv>o major NSF-led programs: WOCE, con-cerned >vith basin»cale ocean circuLation, and theGlobal Ocean Flux Study GOFS!, concerned with»urface fluxes in the global ocean. These program»ofter important <>pportunitie» for cooperatii e efforts» ith NOAA progran>». With leveraged interagencvetfort», achievement of the predictive goal» of theNOAA program becomes feasible. Theretore, it i»umportant that NOAA have its main programmatic

thrusts on both interannual and interdecad,al ocean-

climate variability in place by thc carlv 1990's. I'ig-ure 4 shows the existence of these Cooperative Pro-gram Effort» CPE! for the decade of the 1990'».

STACS, concerned with deriving climate indic«»for western boundarv current phenomena, i»»hownin Figurc 4 a», more or less, operating off-line bvitself bef<>rv interacting with the interannual andinterdecadal ocean-climate progra<n clement» in tlaccarlv 1990'». Bv that time, STACS will have accumu-lated about a decade of time serie» nccdcd to add re»»the cro»»-effects between the interdecaclal and inter-

annual time»«ale», particularlv in thc»ub-tropic», intinac to .nteract with the ncw clenaent» dv»igned t<>address these questions in the early 1990'».

TOGA probably can not answer all of thc inapor-tant res» >rch questions coracerning th» ocean» role ininterannual climate variability ivithin existing levelsof resources and within a single decade. A folloiv-<>npr<>gram will need to continue invc»tigation» into tlacmore complex issues of higher latitude response»and the global ocean that may hax«been»tartcdunder TOGA.

Thc f ollow-on program is tentatively namedInterannual Variability I'rogram IAVI'! Figure 4!.In actuality, it may be an expansion and extension <ifTOGA. I hebroader based program must build uponboth EP ?CS and STACS, rather than mainlv EPOCSas ha» bccn the initi«1 situation with TOGA. Also,this program will need to interact i~ith a NOAAinterdecadal ocean variabilitv program elenient laav-ing an Atlantic Ocean f<>cu» scc Figure 4!. Activitie»di»cussed below could be initiated, either a» part of anew int»rannual vari<ability progr'>m, or u»dcr thelater»tagc» of the present TOGA ef fort.

Tlae EPOCS, TOGA and thc STAGS program» needto be enlaanced bv observation» in ncw areas, ~x hilccontinuing observations in select<d areas alreadvexplored on an operational monit<iring b<asis. Thearea of Fl'OCS,and TOGA or po»t-TOGA! re»«archshould be expanded poleward to include intcracti<>n»of thc equatorial/tropical circulation systems andsubtropi«al gvre circulation in both thc Atlantii: a>idPacific, and thc area of STACS concern should beincreased equatorward for the same rca»on. The sameobscrvat><an<al framework applied in the earlier»tagesof STACS and TOGA should be us< d in the enhancc-<ncnt: two to thrcc vear» of intcnsiv» <ib»crving peri-ods should be directed >t identifying important in-dices «n<'I the methodology to monitor the indices.

Prioritv al»<> must be given to full expansion ofmonitoring and rese<arch effort into the Atlantic andIndian O«»an ba»ins, in order to examin» the po»-

sible r<ile of ocean processes in these areas in African,and Brazilian drought, and the effect on ENSO otii at»r m,ass exchange between the Indian an,olving mid-and-highlatitude» will probablv remain a conundrum, so longas the observational framework remains confined to

thc traditional TOGA + 40 degre»s latitude band,and mainlv in thc I'acitic/Indian Oc»an Basins, Inaddition to expansion of observafional network»,c<i<ipcration between prograna elements focusing onboth interannual and intcrdecadal x ariability Fig-ur». 4! xvill be e»sential for progress in understandingthc true cau»al mechanisms for the tvl»conn«ction».

%1eridi<anal circulation involves the overturning<if the ocean. It brings into play both the»urfacv andint»rmediat< lavers of the ocean and thc d«ep andbottom I aver». H<. nce, the aspects of the ocean circu-lation that relate to intcrannual and int»rdecadal phc-nomcna must be connected through the meridional«irculation. Recent model and ob»ervational results

»uggv»t that i~e need to have a better understandingof the meridional heat transport from th» tropics andit» ~ ari<abilitv, For instance, »omc model siniu]ation»ot the ocean indicate that the time»calc of EI Kino

evviit» i» determined bv, the heat loss from thc trop-ic» during a xvarm episode and, the time required torcplcni»h the western Pacific <varm pool.

%1eridional heat transport is crucial in both thec<i<iling and warming processes of the gl<>bal climateheat engine. In the Atlantic, unlike thv I'acific, th»rci» considerable northivard heat flux >cro»» the cqua-t<ir, related to the thermohaline circulation in that

b,>»in. Vari, ability in this cros»-equatorial flux willla 1v« important implications to heat flux further north,In both ba»ins, processes on the we»tern boundarya pp >rc>atlv have a large influence on meridional heattlux. A better understanding of thc interaction be-t>veen thv «quatorial circulation and the subtropicalgyre», ivith particular emphasis <>n the westernbound aries, is required.

Thc meridional heat flux away from the equator inthe tr<ipic» and the cross equatorial heat/chemicalfracvr flux»» are kcv components ot' the global de-scriptiori of ocean circulation required bv globalcha ngc»tudi«». Measurement of these transports nearth» «quator requires that special consideration bcgix.«n to the likelv importance of boundarv condi-

tions particularly in the Atlantic!, abyssal circula-tion, and the failure of the geostrophic approxima-tion at the equator. However, coupling a deepcirculation study to the upper ocean TOGA or post-TOGA! program, as indicated by the various inter-annual and interdecadal program interactions in Fig-ure 4, and utilizing the satellite altimeter and windfields available during WOCE will permit a coordi-nated attack on this problem.

The meridional velocities generally are smallcompared to the prominent zonal currents, A combi-nation of direct and indirect techniques are going tobe required to estimate these flows. The programwill require:

~ Zonal transects at tropical latitudes +10'! tomeasure density and chemical tracer distribu-tions. These sections should be repeated afterabout five years, with modifications based uponwhat has been learned in the intervening periodof time.

~ Meridional cross equatorial transects �0'N to10'S! of tracers in the western, central and east-ern regions. Enhancement of the TOGA/Post-TOGA upper ocean thermal field measurementprogram by including salinity measurements.Determination of surface currents with surface

drifters and satellite altimetry; constant leveldrifters may also be needed in very high lati-tudes.

~ Determination of surface wind fields and wind

stress using satellite based scatterometer instru-ments and island meteorological stations in thosebroad areas of the oceans where the thermohal-

ine circulation is believed to be at the surface or

within the mixed layer.< Integration of the above measurements with the

GFDL high resolution model in order to esti-mate meridional transports and refine the over-all picture.

~ Exploration of eddy variability in tropical re-gions and assessment of the importance of eddyheat flux.

Long-term monitoring would then follow the ex-ploratory studies. Other aspects of the research effortdirected toward questions related to the meridionalcirculation and its relationship to interdecadal andinterannual research elements are discussed in Sec-

tion 4,2.

Following the over-all programmatic strategy out-lined in Section 2.0, the next emphasis should be onthe decadal, interdecadal and longer time scale oceanprocesses including possible mechanisms of poten-tially rapid climate change. The important role thatthe Atlantic Ocean Basin appears to play in and thethermohaline circulation and the importance of theinterdecadal signal in the climate of neighboring landareas of the North Atlantic make it high priority asan early focus of research into the interdecadal oceanvariability problem. However, when we look at theimplied scope of the program, involving both theSouthern and Northern Atlantic Oceans, includingpolar and near-polar regions, as well as the equato-rial ocean area with emphasis now including deepwater processes!, the task remains great. Further-more, NOAA lacks experience in some of these areas,such as the Antarctic/Southern Ocean.

One practical solution is to create a highly lever-aged NOAA program, strongly cooperative withother mostly non-NOAA! programs scheduled toget underway in the early 1990's. Since the NOAAobjectives are, for the most part, not the same asthose of the other programs, the NOAA effort cannot simply depend passively upon the non-NOAAefforts. The other non-NOAA programs are more ofa pure research nature, in which understanding ofprocesses and overall dynamics is the main goal,although guided by climate concerns to some de-gree. However, NOAA's efforts must be directed atdevelopment of predictive capability for the climatesystem on longer time-scales, and establishing theessential base-line observational networks needed

for the diagnostic and predictive applications. To dothis, the NOAA program must also be long-term.

In many ways, the Atlantic Basin Variability ABVP! effort identified in Figure 4 is an analogy ofTOGA, but there are essential differences. TOGA isan intense ten-year effort, built upon a strong on-going base funded NOAA effort in the Pacific

EI'OCS! whicla is directed to «rre c}cre.»ticrn». Th«AI3VI' effort will build upon STAGS t<i »ome degrcc,but nau»t provide continuing funding tor tlac <ithercore effort TTO!, that ha» never been I'<irmallifuiidcid. I he ocean tracer work mii»t noii,also Iae

applied on « long-term basis in thc Atlaritic it ha»bccn ongoing in the Pacitic!, specific, illy f<ir thc i ntcr-decadal problem.

The A13VP must form a pcrnaanent «<ire programcontimiing through to an expanded glob,il o«eanintcrdcca.ial i ariability focused rcse;ir«h eff<irt some-time later in thc 1990's. Tent«tivcli, this expandedfocus is»lioii n as a new program el<.'ment, thc Inter-decadal Variabilitv Program IDVI'!, in Figure 4.

In the context of understand irig th» mean «iriula-tion, intcrdccadal changes, and thc mcridi<inil tr«ra»-ports of he«t and gases, it is clear th«t studic» rcl,ate<1to global «limate change miist include the intermedi-ate and deep circulation» and their interactions.Modeling ha» been verv successful in»imula ting thcupper cq:iatorial ocean iri the TOGA I'rogram, butthe deep iviter circulation has rc«eived les» atten-tion. It is known, however, that thc nicridional oi'er-turning an<1 deep floivs across the eiluator plav;ivery important role in the global heat balance. In thcAtlantic, the mr..an annual heat flux i» nortlaii ar<1across thc equator, a dramatic contrast to the»vm-metrical "aoleward pattern in the I'acific. Dcc,ad«1changes in this flux have been sugge»tcd a»,i mech,a-nism tor f<rrcing atmospheric circulation «h«ngc».Major regional climate questions siiih «s thc»our«eof rainfall variibilitv in thc Sahcl, northea»t 13raziland the I '.S. Great I'lain» may be intimatclv tied toocean vari«bilitv in the Atlantic basin.

More»pecificallv, recent paleoclim,itic studies havesubstiinti<'<ted the variability of North Atl,antic thcr-moh«line circulation as a major factor in the initi«-tion of ivarnaing and cooling event» <ib»crvcd in theclim«t» record. This is supported bv coupled <iiian-atrnosphcrc riiodel results that sugge»t that thi glob,ilcliiaa«te si stem mav be chara«terizc<1 bv tivo st«blestates that differ primarilv bv the pre»ence or «b-sence of the global «irculation cell,associate<1 ii.ithNorth Atl«ntic deep water formation. Thc gc ogr,iphi<constraint of the areas of deep water formation bi ingin the Atl;inti«suggest this rcgi<7n «» an area ot carlvemphasi».

In the Atlantic, the considerable northivard heatflux «cross the equator na«v bc rclateil t<> thc thcriaao-halinc circ ul«tion in that basin. 'I hcrcforc, i ariabilitvin this eros»-ec}uatorial flux <vill liavc import,intimpli«ation» to heat flux furtlier north.

Ill bcitli flic.' Atlcliitl««nd I acrtl«1'«»lra», pr'<i< essesI in l lie ii estern bound,aries app«rcntli' ha i c,i I« ig«infliicncc on meridion«1 hect flux. A bc ttcr under-

»t«rid<rig <if tlac iiatci';l«tiola beta«<'cra lie cq<1<i <!i l,iliircul.iti<in;ind tlie»ubtropical gvres, ii ith parti«ul«r<na}al«i»i» on thc ivestern boundaries, i» «Ie«rlv ri-iluired.

Tl'ic i'crtlc;cl pa'tliivavs between tl'ic.' »el i f i«c lridi1ccpcr l«vcr» of the occ'«n must be ni<idc'llcd ciir-rc«tli in <irder to»imulatc the efteits <rr «tria<a»pherieiarh<in dioxide on climate arid nitur.al ilim«tc v,ari-

ibiliti on longer time sciile». Thc mci»t i ilu.able d«t,afact» fear ieritiing that thc iertical pathiv«vs havebeen in«luded in o«can «irculation in<i<1cl» corrcctli

,irc me.a»urc ments of transient tr«c r» su< Ii «» thc

!re<in», tritium ind bomb-producci1 iarb<in-14. F' oir.hi» reason lie transient tr«ccr pnigraiii in IVOGE isof p,rrticcrl,ar importance for thc contmueddev< l<ip-iiicnt ot NOAA iiaodcls.

The trcon me«surement» taken bi UOAA in it»

<iw n TT .! progr ina in the N<irth I'a«ifi«are,a uniquere»<iur«c in thi» re»pe«r, ind thi» pr<i ram»hould»cri i a» thc basis for simil,ar <ibscri,iti< n» in the At-

I a rltl« iilld iri par tie'U I 1 i, tlao»e Iiigli lrltltcldc «rcca» N<irth «nd South in the Atl«ntic Ba»in ~ <chere deepii' it«r reneiv«}occurs. Actii itic» in tlrc Arat arctic and

Iii i'li I atitudcs ot' the North Atlantic,,a»«rc i atcd ivithdccp ii «ter t<irmations and the thi rnioli,ili»i circula-tioii, <vill ini olie. extensive NOAA p,rrtr«ipati<ira in<ithcr pnigram» on an intcniational bi»is.

Aiiothcr component of the e«rlv Atl,iriti« i ari,ibil-iti,a< tivitic» ii ill be initiation of iin Atl llilic i <>Iura-

tccr Ob»crviiig Ship VOS'! pnigr«m, »iinilcir in»v»-tcm i1c»ign to the VOS program ii.hi«h h«» bccrai»i il<iabli' in thc suppcirt cif TOGA I',ii:tie .i«tii itic».I lii' pro}iil»cd Atl iiitlc VOS will pr<ii id» improi cdcippcr <i<can thermal f'iclds f<ir;traao»phere-<iie,iniiitcr,iiti<in «tudie».

It should bc' noted theat deep XI3l. <<nit» «re rioii«iaiil,able, but;irc con»icleribly nicire c<r»tiv th«ii thc»t,l i i<'Iiln1 <!iae» Ii<!ii ii idi lv il»e<1. I Icra«ci tile' dc<.'p«pplr«,atr<ira uraits <vill pnib«blv need Ii be' «<inceri-tratcd in the ieri high latitud» «nd cqii,itori,il .ire,i»c mpla«»ized here, «nd if <applied el»< ii hcn, ii illpriib,iblv race<1 to be "«<r«r»elv" iiitcr»per»cd ii:ithitia lac}r<rd XI3T iliilf». Ob»cI va tlotas ilia<, raa<!lar t<rr iiigstr itcgie»,arc iaaaclc «ost-eftectii c bi,ipplvin ~ re siilts<~f nioilcling <ii,agnostic studic» of the»i stem» lacing~a ri<a li'zc<1.

Separation of thc intcrannual and interdecadalvariability effects is only a con<, enient artifact of theprogrammatic»trategv constrained by limited re-source». Clean separation of phvsical processes andcirculation based on characteristic frcquencv is onlyapproximate. Consequently, a later res«arch f<icus,perhaps an independent progra m element, ultimatelymay be needed to address the full range of question»concerning the combined inter<innual through inter-decadal climate variabilities on a true "global ocean-global atmosphere" basis. This i» tentatively dcsig-iiated in Figurc 4 as Gl<ibal Ocean Variability andClimate GOVAC! for startup in the 199S-2000 timeframe. FIowevcr, certain critical questions will re-iluire coordination of interannual and i»terdecadalresearch efforts prior to that time.

The internal iNOAA ocean-circulation related pro-grams that will support thc ABV1' effort arcSTACS,ivhich already hasbccn dealing ~ ith long-term mea-siirements of gvre variability in thc Sub-tropical At-lantic, EPOCS and TOGA/I'ost-TOGA Section 3,0!,w hich must deal with the equatorial Atlantic and themid- latitude connections on intcrannual time scales

that are stronglv coupled with the interdccadal cf-I'ccts ot gvre dynamics and interactions in the Atlan-tic tropical areas. Anv TOGA 'Post-TOC A Atlanticiariability work will need to be well coordinatedivith the ABVI' effort. A possible example of such aioordinated TOGA-ABVP proj ct might concern thebranching of the Atlantic Equatorial C«rre»t at thegeographical "nose" area of Ifrazil, between S de-grees and 8 degrees S latitude. North or South shittsin the axis of thc branching current system mill affectthe transport of warm South Atlantic water into theCaribbean and the Gulf Stream I.amb, 1972! andc<insequcntly is related to both interannual and inter-decadal climate variability in the Atlantic basin. There

,ilso remains a po»sibility of an international pro-gram effort <if some kind in Ihis area, that mouldallow broader based cooperative efforts, Again theNOAA concerns would be directed toward the long-term and dcvelopriient of predictive capabilities.

I.i<st, in the Atlantic, the objective is to deriveindices for such cross-equatorial, ivestern b<iundaryfciturcs as the Deep Western Boundar> Current amajor c<imponcnt of the thcrmohaline circulation ofth» North Atlanticl and surface currents, Modelingand obscrvitionxl studies suggest that both of thesefciturcs play an important role in meridional heatfI«x. During the intensive observing period, directcurrent, water mass and mater mass «ge <ibserva-tions ncid to be taken. To trace miter misses, an

inilicati<in of cross-equatorial flow, nulrients e.g.,silicat«and phosphate! coupled with oxygen need t<ibc usci1. To study water ma»s age», helium/tritiumrati<i» t<ir sh<irt time scilcs months to vears! and

halocarbons for longer time scales decades! need tobc <>ppli< d. I he fatter approach ha» rcc«ntly been«ti i~ed to trace Deep Western Boundary Currentmater» ai ro»» the «quator.

I.at«r <i» in the I'acific, the strategic <ir<phasis»h<iuld uicluilc intermediate mater mass formation.

In ii>ntrist to the Atlantic, there is apparently node<'p <eater f<irmation in the . North Pacific, Thus, bypniccss of elimination, meridional heat flux is proba-blx stro»glv related to circulation of intermediateivat«i». I'roccss studies in the critical form, stion re-

gions of these <eaters, and large-scale mapping oftheir distribution using tracers, are required. In theapproach described here, the heat flux awav fro<r< thec<1«ator an<1 the cross equatorial heat/chemical tracertlux«s irc kcy components of the global descriptionof occa» circiilation required bv global climate changestudie», Aspects of research concerned w ith themeridional circulati<in have been discussed in Sec-

tio» 3..x

A ma!or part of the pr<iblem confronting humaninstituti<in» i» making use of climate f<ireca»ts is thatgl<ibal ai eragc conditions have little mcani»g locally. . en«ra llv, a local or regional manifestation of a globalcli,inge i» signific,intlv more extreme than the globalai cragc. Our insights into the regional inipli«ationsof glob il change are not x~ ell developed. Thc impe-t«» f»r this line of research is the long-tc rm ten ye irs<ir I<ingcr! cco! ogical conseiluences and the »car-termhiim,iii impacts less thin tcn years! resulting from

bottom pressure gauge», cl<>»e'..y spaced m<>ored ar-rays intensive transport array! of current meter»,temperature and conductivity sensors, Ship basedCTD profiles to the bottom and XBT ca»t» iv<iuld betaken on all lines. Oceanic tracer sample» arc alsoproposed in these areas.

The three "choke point" lines are clear candidatesfor a possible cooperative effort by NOAA, as is theocean tracer ~vork.

An E-M cable system i» not mentioned a» part <>fthe long-term Drake Passage monitoring system, sothat STACS and the ABVP ma>, be able to contribute

such a system in a joint effort. It should also be notedthat W. Emery ran hydrographic surveys c»scntiallv,>long some of thc»arne lines about a decade ago a»part of the FGGE Program, so that a baseline, in part,ilready exists. NOAA could support repeats of t'heselines on a regular, long-term basis as part of thcABVP Program and contribution to WOCE.

The Cvrc Dynamics Expcrirnent part ot the inter-national WOCE WOCE Core 3, 1987! appears to befocusing on thc North Atlantic, perhap» with someSouth Atlantic work and a possible deep circulationexperiment in the Brazil Basin. The concerns appearto be highly compatible with the A13VP strategv.There will be a component «f the Core 3 effort con-cerned with meridional circular ion and deep convec-tion driven by diabatic processes as involved in bothdeep water formation in the sub-polar areas and warmIS degree v'atcr formation in the sub-tropic».

Another Core 3 concern involves the sub-polarfrontal exchanges at the boundary of the sub-tropicalind sub-polar gvres!. Tracer <work is al»o proposedalong with hydrographic survcvs, velocity float» andmoored systems. The NOAA concerns in ABVI'<vould seem to stress gyre interactions in both theequatorial/tropicai area and high latitudes in both»outhern and northern hemisphcrcs. Thc surfacelronts at the boundaries of th: »ubpolar gyre» and»ubtropical gyres in both the Northern and Southernhemisphere are singled out for special attention. Theseinteractions are a»»ociated in thc South Atlantic with

the important convergence zone near the AntarcticCircumpolar Current. Hence, cooperative opportu-nitics with Core 3 efforts appear promising. Also,STACS-type cable systems are not explicitlv listedfor Core 3, so that this could provide a unique NOAAcontribution to any coopcrativ» effort. Also, the areaof WOCE concern» cut» off at the 60 degree N lati-tude line, whereas NOAA interests will go to stillhigher latitudes. NOAA's contribution to a coopera-tive effort could involve deterr<>ination of the North-

ern boundary conditions for the WOCE efforts.

I h<. Arctic Ocean Sciences Board NAS, 1977! ha»

propo»ed a Greenland Sea Project GSP! whichhas anumber of international participants, including cer-tain science funding or policy levels of governments,other than thc Vnitcd States. Given thc similar inter-

e»t» betw een the prop<>sed GSP and the Atlantic vari-ability strategy outlined here, NOAA would be alogical candidate to undertake the V.S. agcncv role.The project's region of study is consistent with theidentified «rea tor NOAA'» North Atlantic climate

concerns.

T' hc project is concerned with xvater ma»» produc-t i<in, sea ice variabilitv and it» relationship ttmo»phcric exchanges driving the»v»tern. Geo-chemical tracer <york, modeling, deploy ment ofmoored arravs of current meters, tracked»urfaced rifters, pre»»ure gauges are all proposed. I I<uvcvcr,E-M cable efforts arc not explicitly pr<iposed. Thepas»agc» bet~veen Iceland and Greenland 1nd be-tween Spit»bergen and Greenland offer potential lo-cations lor such deplovment», although thc othersides of Greenland and Spitzbergcn facing NorthernEurope pose more design questions and implemen-tation problem». Agai~, STACS technology, or ad-vanced development» of that technology »< e Section~.0!, mav be applicable here, a» would NOAA tran-»ient tracer ivork and related carbon dioxide flux and

ocean procc»s research.

The . JSF-Ied Global Ocean Flux Stud~ GOFS!

project Brc~~ cr, 198t>! i» concerned with a varictv ofsurface processe» and fluxcs, including those involv-ing carbon dioxide. The >NOAA program must bcco>>cerned with surface fluxcs of fresh water, Intent

and scnsiblc heat, and carbon dioxide, so that mutu-ally a<ivantagcous inter-relations bet~veen the Atlan-tic component of GOFS and the NOAA program»<cm both feasible and desirable. In this respect, theNOAA effort mav bc able to complement GOFS bvconcentrating on the ocean margins and the shore-%yard ecl gcs of thc oc<.'a n boundarv currents bothK<'»tern,incl ca»te1 r1!.

There is evidence of a long-term trend in the timeseries of some climatic variables over the past cen-tury or so. However, the earliest studies by Fletcher,Radok and Slutz �979! indicated that climate vari-ability on the decadal to centuries time scale is domi-nated by only a few abrupt adjustments of the circu-lation regime, rather than by gradual change. Theevidence of the greatly expanded COADS data setnow reinforces that conclusion. However, questionshave lingered about possible systematic errors dueto changes in measurement technology and prac-tices, and the transition from sailing vessels to steampowered ships. Every effort has been made over theyears to identify and remove sources of systematicerror, but it is difficult to prove that no systematicerror sources remain when one cannot repeat theobservations under controlled conditions.

Consequently, efforts are continuing to comparethe COADS data with indirect historical and paleo-climatic evidence. These are mostly from land areas,and range from the historical record of Nile Riverflood levels at Cairo, lake sediments in Africa, andice core data. The records generally show changes ofan abrupt nature correlated with the transitions indi-cated in the COADS series. One implication of theobserved sudden transitions is that we need muchlonger retrospective time-series for numerical modeldevelopment and verification purposes. Longeroceanic retrospective time-series are preferred overland series, as being more directly indicative of pastocean circulation patterns.

Since we have mostly reached the historical limitsof scientific observations with COADS, indirectsources will be required. Since these indirect sourcesare inherently very "noisy" data that are difficult tointerpret, redundancy of many data types will beneeded to produce statistically based reliability intheir interpretation. Ship logs may be one source, butthere is another. Man has been fishing on the oceansurface for as long as he has been sailing upon it, andfish catch and whaling records indicating changes inspecies populations and their patterns of behaviorexist going back centuries. These records overlapwith the COADS data in some of the same areas since

the nineteenth century. These can also be correlatedwith studies of mud layers varves! in areas wheresedimentation rates are laid down ten or more times

as rapidly as the world average ocean sedimentation

rate. It may be possible to calibrate fish scales andother paleo-biological evidence in the varves bycomparison with written historical fish populationrecords and the whole sequence of overlapping di-rect and indirect ocean records, beginning withCOADS Sharp and De Vries, 1988!. In principal atleast, these can be extended back for several millen-nia. Such a paleo-biological component of a compre-hensive NOAA Climate and Global Change Programneeds to be developed Figure 4!.

The strategic approach involves the application ofthese long time series with computer simulationmodels. If sudden changes are indeed characteristicof climate change on interdecadal and longer timescales, there will be a particular problem in simulat-ing the actual transition processes. Typically, a non-linear system undergoing such a transition, reorgan-izes itself so that boundary layer processes and othersub-grid effects become critical, at least during thetransition, Unfortunately, lack of resolution of themodels leads to parameterizations that are usuallybased upon assumptions dependent upon the exist-ing state of the system, which may be incompatiblewith transitional conditions and the future state.

An atmospheric GCM, or ocean circulation model,is simply a discretization of the known equations ofmotion of the atmosphere or ocean!, with physicalprocesses treated explicitly when possible radiation,orography, large scale precipitation, etc.!, and param-eterized when necessary cumulus convection, smallscale mixing, etc,!. The mix between explicitly com-puted and parameterized processes changes as theresolution increases. For example, if the resolutioncould be refined to one kilometer, it would no longerbe necessary to parameterize cumulus clouds be-cause they would be explicitly resolved. Since modelresolution is purely a function of the capability ofcomputer technology, we can expect models to im-prove as advances in computer technology allowhigher resolution. This progress will be slow, sinceevery doubling of resolution involves 16 times morecomputation. Doubling of the resolution in each ofthe two horizontal spatial dimensions, multiplied bythe mandatory reduction in the temporal step size,and assuming that the number of vertical layers inthe model is also doubled, accounts for the factor of16.

A national effort is being made to develop super-computers, and climate modeling is considered to bethe prime nondefense application of these machines.NOAA will need to update its computing facilities asthese new generation machines become available.This will require a more frequent updating of GFDL

computer» fn>m the present ten-vear cycle to an ac-celerated five- year cycle or less as dictated bv theactual advanc»s ir. computer systenis, if we are to,ichieve important modeling capabilities, such, is»imulation of trin»ition regimes betw»»n climate»tates.

It i» imperative that XOAA continue to develop,on a more systematic basis, technology for monitor-ing climaticallv important oceanographic processes.Both shipboard and i» sit>< instrumentation are r»-quired. In particular, an acoustic Doppler vel<>citvprofiler which can he deployed on ships of opportu-nitv is needed to provide g.'.obal distributions ofsurface velocities, an important variabl» for climitemodel validation. Similirlv, accurate m»teorologicalpackages, including sensors to d»t»rmine»urf<iceenergv fluxe», are r»quired for installation on ships-<>f-opportunity,

A "scientific cable" is necessary for use in loca-

tions other than straits and passages wh»r» la>i-tt-l,ind connections are possible The cable»houkd bedesigned to provid» data on the internal structure otthe ocean, rather than merely total transport, as doesthe present cable system. A possible arriy wouldconsist of suites o. instruments connected bv cabl»

and having r»rnot»ly programmabl<i sen»or packageslocated at selected positions on the»eaflo<ir,

Other electromagnetic methods for mea»uringlarge-scale v iriations in ocean transport ar» promis-ing. The el»ctromagnetic methods that are ideal can-didates f' or meisurements of ocean transport v<iri-,itions are: I! voltage measurements using passiveor active telephone»ubrnarine cables tlia t span oceancurrents, �! bottom horirontal electric field m»a-»urements, �! surfice and bottom vertical electrict'i»ld measurements, �! botto>n horizontal mign»tict'ield measur»ment», and �! .iccuratelv towed elec-tric field measurement».

Cross stream cable voltag< meisurements vieldiccurate and continuous real lime measurement» <>f

the transport variations in the Florida Current. Thedevelopment of Inexpensive c;ible laving techniquestherefore should b» started for continuouslv moni-

toring the transport variations of oth»r importantocean currents. The us» of »xisting submarine t»I»-phone cabl»s should also continue to b» explored a»these measurements will be lli» least expensive ofiiiy of tli» electromagnetic methods, Trans-oceanic

t»leph<in«c«ble» niight vield direct »vidence of h»<itflux v <ri ition» if long period temperature,ind otherpos»ibl» noise of the power stations c<in be accuritelyni< ill it<. >r«'k.

Th» point »l»ctromagnetic mea»urem»nt», devel-<ip»d,ind»ucce»»tullv used in deep ocea>i magne-t<>l»IIuric studies, miv also prove to be valuaN» b»-cau»e ot th» inherent spatial »rnoothing verticallv,ind h<irizontallv! of the el»ctromagn»tic»igna I» andth» low»r costs of depl<>vment compared to installing<.ahie». An irray ot bottom magnetic and electricm»isur»m»nts should he tested a» an alternative to

cni»»»tream cable i oltage». Such arrav» will be u»»-tul in r»gi<ins such as the Arctic wh»re it i» n<>t fea-»ibl» to in»till long cable».

Th» i ertic il »lectric field is useful, is,i measure of

th» magnetic ea»t we»t tr,in»port, but will not pro-vid».ini h<>rizont il spatial averaging since the i erti-c,il »l»ctric currents are small due to the eft»cts of the

in»ulitiiig,itm<i»phere. Such measurements wouldh» parti<. ul«rlv useful in the equatoriil region» wherethe tlo« i» predominantly east-west.

Finally, accurately towed electric fiekd me<sure-m»nts will provide the imp<>rtant regional »urv»v ofthe <i<.e,in curr»nts; namely, its extent and spitiali iri itions. This intormation will be n»ed»d to d»signth< minimum cabIe length and the maximuni »pac-ing allow»d beti~ »en the»ea floor point »lectro-m,ign»tic rec<irders,

'A'ith th» <l»velopment of a pre<iictiv» capabilityf<ir «lim«t» cli<inges taking place ov»r a ringe of timesc,il»»,i»,i goal, the concept of the climate»v»teni as a"he,it »ngin»" with tivo iv<>rking fluids th< atmo-»ph»r»,ind th» o=ean»! provides an effective meta-ph<ir for tormulating the critical questions th,it mustb» an»i< er»d. The qu»stions can be structured into ahierarclii going from the most general to th» verv»p»cific. At the top <>f the hierarchy, the m<>»t generalqu»»tion c<>ncerns the temporal and»pitial variabil-ity <if both the effective forcing fi»lds and the vari-,ibilitv <it the re»pons» of the two working fluids ondiff»r»nt characteristic time scales,

Th» r»»»arch»lrategy is designed to .inswer theimp<>rtant qu»stions. At the most gen»ral l»vel <ifipproach, the»tritegy sc»ks to recover retro»pectiveinl<>rmation on the past behavior of the climat»»y»-t»m and to u»e thi» information, alo>ig ivith dat,ifnim present monitoring sy»tern», t<>r »<libration,initial c<indition» and b<iundary condition» for com-

puter simulation models of thc climate system. Thecomputer simulation models involve thc coupling oithe atmospheric and ocea nic general circula tions andthe interictions with the land areas of the earth and

cryosphere. The simulati<in models must be sequen-tially refined in an iterat:.i e process from the infor-mation gained through focused process reseircli, di-agnostic studies and vigorous comparisons of siniu-lation results with knovvn past climatic variability:patterns,ind current data from monitoring systems,Predictions emerge from:his process by numericallvcarrying forvvard in time the projections of the cali-brated and validated model».

Knowledge of the characteristics of the climatesignil on different time scales and in the difficultregions of thc world oceans allover ordering of theresearch priorities and structuring of the researchinto programmatic component». A plan involvingthe development of a sequence of programmatic stepsis suiiimarized in Figure 4.0. While the program unitsshown are not intended to be definitive at this time,the questions that they are designed to answer irccritical and the programmatic structure supp >rtirigthe research strategy that is formally idoptei1 >villneed to provide those ansivers.

A specific icscarch issue of importance that coii-cerns the rol of the oceans in intcrannual climate

variability is the effect on EXSO of vvater mas» ex-changes between the Indian and I'acific Oceans. C?ninterdccadal,ind longer time scales, important re-search concerns include: i',1! the role of Ixiorth Atlan-

tic deep water formation, and exchanges vvith thenorthern branches of the.,ubtropical gyre, in re gulat-ing the thermohaline circi ilation, and i21 the identifi-cation of feedback control mechanism» in the Atlan-

tic therrnohaline circulation and their role in possiblemajor, and relatively sudden, climate changes takingplace on the century time scale. On both interannuaIand interdecadal time scales, some of the importantresearch questions relate to: 11! understanding tlicdynaniics of the ocean/atmosphere fluxcs of' he,it,moisture and niomentum, particularly with respectto areas controlling tlie time- variabilitv of vvatermass formation, �! the relationship of changes ofheat content of the equatorial zones and cli,inge» inthe position of the ITCZ and their relationship toclimate variabilitv in higl.er latitudes, particularly inthe Atlantic basin.

Other questions, some niore specific and somemore general, have also b< en posed. Still, other qucs-tioris wiII emerge from the learning pr >cess of tlicresearch itself.

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