Synoptic and seasonal variations of the ice-ocean circulation in the Arctic: a nunterical study

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1 Annls of Glciology IC> Interntionl Glciologicl Society Synoptic nd sesonl vritions of the ice-ocen circultion in the Arctic: nuntericl study ALEX WARN-VARNAS SAGLANT Reserch Genter, L Spe<.i, Itly RICHARD ALLARD Berkeley Reserch Assocites, Springfield, VA, U.S.A. STEVE PIACSEK Nvy Ocen nd Atmospheric Reserch Lortory, Stennis Spce Genter, MA, U.S.A. ABSTRACT. The circultions of the Arctic ice cover nd ocen re investigted using coupled ice-ocen model. The coupling is strong nd two-wy for synoptic time scles, ut is limited on sesonl time scles: the geostrophic ocen currents re not chnged y the computed het nd slt fluxes. The ice-drift motion, Ekmn trnsports nd the wind-driven prt of the rotropic circultion re exmined for the months of Ferury nd August 1986, representing different tmospheric forcing, icethickness nd ice-strength regimes. Initil exmintion of the results reveled no significnt sesonl dependence of ice-drift response on the synoptic time scle, other thn lrger velocities with lrger wind stresses. Dily mximum ice-drift velocities rnge from 20-40cms- 1 in Ferury, nd l5-30cms- 1 in August. The corresponding men monthly mximum drifts were II nd 9 cm, respectively. The drg ssocited with the geostrophic currents plys much igger role in the summer ecuse of the lighter tmospheric stresses. The well-known reversl of the normlly clockwise Beufort Gyre to cyclonic system in August tkes plce in few dys nd lsts well into Septemer. In Ferury, the Beufort Gyre vries etween lrge, clockwise system covering ll the Cndin Bsin to smll, tight gyre centered over the southern Beufort Se, without ny hint of reversl or disppernce. Lrge res of strong divergence were found in the Ekmn trnsport ptterns, s well s the icedivergence fields, indicting res where ice thinning, openings nd new ice formtion might occur. In August this occurred in the Chukchi Se, nd in Ferury just north of Novy Zemly. INTRODUCTION I t is well known tht the Arctic ice cover cts s n insultor or shield ginst oth het nd momentum trnsfer from the tmosphere to the ocen. This interesting geophysicl process hs een the suject of mny studies. In prticulr, Lemke (1987), Mellor nd Knth (1989) nd Bjork (1989) hve used one-dimensionl models to study the detils of the het nd momentum trnsfer processes, s well s the mintennce of the men verticl structure of the Arctic Bsin. There hve lso een three-dimensionl (3-D) coupled ice-ocen modeling studies y Semtner (1987) nd Hi ier nd Bryn (1987), oth using prognostic ice models ut the ltter using dignostic ocen model. In ech of the 3-D studies, however, the turulent mixed lyer hs een prmeterized in very simple mnner, ssuming constnt lyerdepth to the first su-surfce grid-point. The current study hs imed to improve on this spect of Arctic modeling y introducing n ctive, second-order closure turulent mixed-lyer model under the ice tht is driven y 12 h generl circultion model (GCM)-derived tmospheric momentum nd het fluxes. Although this study involved complete tretment of the thermodynmics nd hydrodynmics of the 3-D ice-ocen system over the yer 1986, the focus of the present pper will e on momentum processes nd circultion. The genertion of ocenic circultion y the curl of the overlying wind stress is non-trivil prolem in n ocen with topogrphy, nd hs een the suject of mny theoreticl nd numericl studies. The presence of n ice cover presents n dditionl compliction nd gives rise to severl questions: how much of the wind curl is trnsmitted to produce circultion in the ocen; how much stress is ville to produce mixing nd Ekmn currents in the surfce lyers under the ice, nd wht is the 54

2 drg experienced y the wter due to ice-form drg nd turulent viscosity? Answers to the lst two questions hve een ddressed t length y McPhee (1982, 1990), ut nswers to the first question re still incomplete, if not lcking, especilly on the oservtionl side. In the upper ocen region (which, in the winter, includes depths down to 500 m or more), the ocenic velocity is superposition of the Ekmn, inertil nd geostrophic velocities. On sesonl time scles, the geostrophic velocity is dominnt, ut there cn e importnt net contriutions to the trnsports from the Ekmn drifts s well, especilly during periods of very high winds, which re common in winter nd spring periods. The reverse question, therefore, is lso of gret interest: to wht extent, nd on wht time scle, do the geostrophic currents modify the ice motion? MODELING APPROACH The coupled ice-ocen model used in these studies contins the Hiler (1979) ice model nd 3-D ocen model tht consists of turulent mixed-lyer model nd n inverse geostrophic model. Coupling etween the three models is chieved s follows: the ice is coupled to the ocen through flux oundry conditions (including het, slt nd momentum); the mixed lyer, in turn, is coupled one-wy to climtologicl ckground ocen, receiving dvection velocities from geostrophic inverse model. There is no direct feedck from the computed temperture nd slinity chnges to the geostrophic currents; i.e. pressure is determined solely from the sesonlly-evolving, predetermined climtologicl density field. The computed Ekmn drift nd Ekmn divergence, however, lso contriute horizontl nd verticl dvection velocities, respectively, to the mixed-lyer model. In prticulr, on the thermodynmic side, the ocen model clcultes the mixed-lyer temperture, freezing temperture nd ocenic het flux for the ice model, wheres the ice model determined the stress etween the ice nd the wter nd the slinity flux under the ice cover. The Hiler ice code ws modified to utilize the mixedlyer tempertures, freezing tempertures nd ocenic het fluxes clculted in the ocen model. The het udget routine includes the seven-level thickness distriution fter Wlsh nd others (1985). On the momentum side, the ocen contriutes velocity to the ice-wter drg tht is the sum of the winddriven Ekmn nd geostrophic velocities. In turn, the ice momentum equtions furnish ice velocities tht enter into the ice-wter drg force. Since full turulent mixed-lyer model is used, we employ the ice-wter drg rther thn the modified wind stress (wind stress minus internl ice stress) s the upper oundry conditions on the ocen (Svensson nd Omstedt, 1990). In open wter regions, the tmospheric fluxes re used directly for the upper oundry conditions. If grid cell is ice-covered, the wind stress nd the het fluxes re pplied to the ice first, nd then the ice-wter drg is computed to drive the ocen. Some dditionl model prticulrs will now e descried. To simulte the evolution of the mixed lyer under the ice nd, in generl, the thermodynmic chnges m the ocen, we hve decided to use the TOPS (Thermodynmic Ocen Prediction System) model tht hs een opertionl t FNOC (Fleet Numericl Ocen Centrl) in Monterey, Cliforni for severl yers (Clncy nd Pollk, 1983). For this study, the model hs een modified to extend to the ocen ottom. The TOPS model employs the Mellor nd Ymd (1974) Level-2.5 turulence-closure method to prmeterize the verticl eddy fluxes of temperture, slinity nd momentum. A wek three-yer relxtion is imposed on the temperture nd slinity fields elow 50 m to prevent the solutions from strying too fr from climtology on long model integrtions. Our tests with lower or zero vlues of this constnt produced no significnt differences in either ice thickness or concentrtion, nd none on the synoptic or monthly time scles (see lso Hi Ier nd Bryn, 1987). The geostrophic velocity t ll levels of the ocen is clculted with et-spirl type inverse method of Peggion (1988), utilizing sesonl density fields derived from the Levitus (1982) climtologicl T nd S fields. The model ssumes the usul hydrosttic nd geostrophic pproximtions, nd dditionl constrints re imposed on the density field due to mss conservtion nd the topogrphy (see Olers nd others, 1985). The resulting liner equtions, fitting ll constrints to the dt, re solved through minimiztion procedure. The computed geostrophic currents re then interpolted to monthly vlues. The entire coupled ice-ocen model is defined t equl grid intervls of 127 km on polr-stereogrphic projection, with totl horizontl resolution of 47 x 25 grid points. The verticl grids of the TOPS nd the inverse models coincide, contining 17 levels in stretched configurtion, with resolution tht plces nine points in the first 100 m nd vries from 5 m ner the surfce to severl hundred meters ner the ottom. The resolution is designed to trck vritions in the mixed lyer, rther thn trck vritions of the ottom topogrphy. This grid lso corresponds to the grid used y the PIPS (Polr Ice Prediction System) of the Nvy in dily opertionl setting (Preller, 1985). In summry, the ice nd the upper ocen re represented prognosticlly, nd the interior ocen dignosticlly. MODEL INITIALIZATION AND FORCING The Levitus (1982) winter climtology is used to initilize the temperture nd slinity fields in the ocen model to depth of 1500 m, nd the nnul climtology is used to set vlues elow tht depth. The initiliztion of the ice cover is ccomplished y doing 3-yer spin-up of n ice-only model (ut using the 1986 fluxes), nd then using the resultnt ice cover nd circultion on the lst dy of yer 3 s the initil ice field on 1 Jnury 1986 of the ice-ocen model, i.e. the first dy of simultion yer one with the coupled model. The model ws forced y 12 h tmospheric fluxes derived from the 1986 NO GAPS glol-nlyzed fields of FNOC. The model domin nd the horizontl grid structure re illustrted in Figure I, nd the topogrphy with the corresponding resolution in Figure 2. Note tht 55

3 ICE-OCEAN MODEL GRID (127 KM) l..- Sesonl vritions of the circultion Fig. 1. The sin geometry nd hori<.ontl grid structure used in the simultions. BOTTOM TOPOGRAPHY (METERS) Fig. 2. The topogrphy if the Arctic-Greenlnd Se sin with 127 km resolution. only the mjor ocen sins nd ridges re resolved with this resolution. The model essentilly reches sttisticl equilirium fter the fourth yer of simultion, in the sense tht in ll spects the model results during simultion yers four nd five evolve lmost identiclly. Thus, the results re nlyzed for the fifth yer. MODEL RESULTS AND ANALYSIS The principl ims of this pper were to study the momentum trnsfer processes nd coupled ice-ocen response to time-dependent winds on the synoptic nd sesonl time scles. The ccompnying model results on ice thickness, ice extent nd the thermohline structure re eing pulished elsewhere (Picsek nd others, 1990). Since the thickness nd compctness of the ice cover vry gretly etween sesons, specific point of interest ws the sesonl dependence of the momentum trnsfer nd trnsient response. Such study my otin, indirectly, n insight into the role of the ice cover in momentum trnsfer etween ir nd wter. Another question concerned the role of the geotrophic ocen currents. 56 They form very stle drg force compred to the highly vrile wind stress so tht, on the monthly nd certinly the sesonl time scle, their effect should e noticele if not pronounced. The results will e grouped ccording to the following themes: () sesonl vritions of the ice nd wter circultion, () synoptic evolution of the circultion, nd (c) effect of the ice cover on generting wter motions. In this short pper we cnnot give n exhustive tretment nd nswers to ll the ove questions, ut will try to highlight ech point y the most illustrtive exmples. Before we egin detiled look t synoptic responses nd vritions tht took plce in the months of Mrch nd August 1986, we will review the corresponding verge monthly circultions in order to plce the synoptic pictures in more fmilir frme of reference. Figures 3 nd 4 disply the wind-velocity nd the icemotion fields for the months of Ferury nd August We use the geostrophic wind-velocity fields t 20 m height insted of the stress fields ecuse they give much etter detils of the circultion in res of wek winds, s the stress hs qudrtic dependence on the wind speed. Keeping the mximum rrow lengths in the respective figures resonle (i.e. non-overlpping nd covering no more thn three neigh oring grid oxes) left us sometimes with rrows too smll to e discerned clerly over lrge res of the domin when the stress ws plotted. Overll, the Ferury winds over the Arctic re composed of lrge nticyclonic gyre over the Cndin Bsin nd strong, wide "trnspolr jet" over the Eursin Bsin, moving from est-centrl Sieri towrd Norwy. Note the highs over the Beufort Se, Bflin Islnd nd the southern Norwegin Se, nd the lrge low pressure re out 20 est of Novy Zemly. The corresponding ice motion (with verge mximum of 11 cm S-I) reflects the overll wind pttern quite ccurtely: the usul nticyclonic Beufort Gyre occupying slightly lrger re thn the overlying high pressure winds, nd wide trnspolr flow prlleling closely the tmospheric trnspolr pttern over lmost the sme domin. The tmosphere in August is chrcterized y two high pressure regions, strong one over the Greenlnd Se nd wek one over the Beufort Se, nd very lrge nd intense cyclonic low over the whole Cndin Bsin. Between this low nd the Greenlnd Se high there runs well-formed "reverse polr jet" from n re est of Greenlnd towrd estern Sieri. The corresponding ice motion consists of strong cyclonic gyre over the centrl Arctic nd n nticyclonic flow in the southern Beufort Se. However, note tht, wheres the res occupied y the lrge cyclonic wind nd ice ptterns re out the sme, the centers of the gyres re seprted considerly nd the stremlines do not coincide s well s they do in Ferury. There is considerle estwrd movement ofice under the western prt of the (here southwrd flowing) reverse polr jet, nd considerle estwrd ice movement cross the northerly winds just north of Greenlnd. We lso note tht the rther well-formed nticyclonic ice motion ( remnnt of the Beufort Gyre?) is locted west of the wek high centered t the westeren end of the

4 Wm- Vms nd others: AVERAGE WIND VELOCITY FOR FEBRUARY-B6 MAXIMUM WIND VELOCITY 10.3 M/SEC ICE VELOCITIES FOR FEBRUARY -B6 MAXIMUM ICE VELOCITY 11.0 CM/ SEC Ic~ocen circultion in the Arctic AVERAGE WIND VELOCITY FOR AUGUST-S6 MAXIMUM WIND VELOCITY 6.2 M/ SEC AVERAGE ICE VELOCITIES FOR AUGUST-56 MAXIMUM ICE VELOC ITY 90 CM / SEC.. ) "-" : I~ GEOSTROPHIC SURFACE CURRENTS FOR AUGUST MAXIMUM VE LOCrTY= 99 CM / SEC d AVERAGE ICE VELOCITIES FOR MARCH-S6 MAXIMUM ICE VELOCITY 15.6 CM/ SEC Fig. 3. The geostrophic wind velocity t 20 m (J, ice-drift motion ( J, nd geostrophic ocen current (c) for the month of Ferury 1986; ice-drift motion for Mrch 1986 (dj. Fig. 4. The geostrophic wind velocity t 20m (J, ice-drift motion ( J, nd geostrophic ocen current (c J for the month of August Cndin Arctic Archipelgo, nd occupies much lrger re thn the winds ssocited with this high. A look t the geostrophic velocity ptterns in August (Fig. 4c) would seem to suggest solution to the discrepncy: strong nticyclonic ocen currents in this region could well supply the missing forcing for this lrge nticyclonic ice gyre. The sme rgument could lso e pplied to the Ferury circultion, where the geotrophic currents (Fig. 3c) seem to reinforce the tmospheric Beufort Gyre to force the strong nti-cyclonic ice drift. However, look t the verge ice velocities in Mrch (Fig. 3d) serves wrning tht the sitution cn ecome more complicted. 57

5 WIND STRESS MAXIMUM STRESS = 0.71 NT/M"2 WIN D STRESS MAXIMUM STRESS = 0.28 NT/ M"2 ICE VELOCITIES CM / SEC ICE VELOCITIES CM / SEC Fig. 5. The wind stress () nd ice-drift motion () for 5 Ferury Fig. 6. The wind stress () nd ice-drift motion () for 8 Ferury Although the Mrch currents re lmost identicl to those in Ferury, there seems to e no evidence of n nticyclonic ice motion in this region, implying tht the strong Mrch winds (verge mximum of 14 m S I) in this re dominte the current drg. Since the mximum verge winds in August re only out 6 m s \ (nd the stress goes qudrtic with speed), we would expect the effects of the geostrophic currents to e much stronger in the summer. Synoptic vritions The synoptic evolution of the wind ptterns nd the corresponding ice motions for Ferury 1986 re illustrted in Figures A creful inspection of ll the dily plots hs reveled the presence of five sic ptterns which lst 3-5 d on the verge, with the 27 Ferury pttern repeting tht of 5 Ferury quite closely. Figure 5(,) shows the wind stress nd ice-drift velocity for 5 Ferury. The strong low pressure system est of Spitsergen drives corresponding strong, cyclonic ice-gyre centered on the sme loction. A wek, estwrdmoving jet north of Greenlnd nd Cnd drives very wide trnspolr ice-drift current, which nrrows nd intensifies upon reching the Frm Strit, prtly due to the southerly winds of the Spitsergen low nd prtly due to the strengthening costl tmospheric jet. Three dys lter on 8 Ferury the sitution is illustrted in Figure 6(,). The winds hve completely chnged: we now hve highs north of Cnd nd northest of Greenlnd nd strong low over the Sierin cost (reminiscent of the verge winds). These highs nd lows drive strong westerly tmospheric jet over the Beufort Se nd wide trnspolr jet south long 20 E towrd the Brents Se. Wheres the ice motion in the Beufort Se closely prllels the winds, it forms wide trnspolr ice drift over the centrl Arctic which is t 30 ngle to the right of the wind. The perennil Beufort Gyre surfces on 11 Ferury (not shown). We illustrte the ice-drift sitution on 12 Ferury (Fig. 7), which shows the presence of dominting nticyclonic gyre over the whole western hlf of the Arctic Bsin nd reverse flow of ice into the Arctic through the Frm Strit. The next dy (Fig. 7) illustrtes n ice-drift configurtion most efficient for trnsporting nd piling up ginst the northern shores of Cnd nd Greenlnd. It consists of lrge nticyclonic (clockwise) gyre over the Cndin hlf of the Arctic Bsin, nd n intense gyre just north of the Frm Strit, driving etween them very strong southwesterly drift-current towrd these shores. The ice velocity on this dy peks t 37 cms 1 nd the mxim tends to occur ner the pole. On 16 Ferury (Fig. 8) the lrge Beufort Gyre hs shrunk to smll, tight ut very energetic gyre nd strong, well-formed trnspolr drift, with lot of ice 58

6 WIND STRESS ICE VELOCITIES CM/SEC ICE VELOCITIES CM / SEC MAXIMUM STRESS = 0.34 NT/ M"2 ICE VELOCITIES CM / SEC Fig. 7. The ice-drift motion for 12 Ferury () nd 13 Ferury (), Fig. 8. The wind stress () nd ice-drift motion () for 16 Ferury exiting through the Frm Strit nd lso into the Brents Se. This ice movement is cused y peculir wind pttern (Fig. 8): very long high pressure ridge cusing winds to form very wide northwesterly strem tht seems to intensify suddenly everywhere s it crosses the 80 N ltitude circle. On this dy the trnspolr ice drift is out 40 to the right of the wind in lmost ll loctions except in the southwest prt of the Beufort Gyre, where the ice drift nd wind re lmost prllel. Figures 9 to 11 disply the synoptic vritions of the winds nd circultions in mid-august Three snpshots of the flow re presented four dys prt, i.e. for the dys 9, 13 nd 17 August, respectively. The tmosphere on 9 August is chrcterized y low south of Icelnd, high over Frnz Josef Lnd nd wek low over Sieri. By 13 Ferury high develops south of Spitsergen, nd the low intensifies off Sieri nd moves towrd the Bering Strit. By 17 Ferury, the Sierin low hs grown tremendously nd covers the lrger prt of the Cndin Bsin. The corresponding ice motion chnges from highly deformed, jet strem-like wve on 9 Ferury to gint cyclonic gyre occupying the most prt of the Cndin Bsin, driven evidently y the lrge low pressure cyclone. This well-estlished reversl of the normlly clockwise Beufort Gyre hs een simulted nd discussed y Preller nd Posey (1989). The strong trnspolr drift, common feture of the ice motion, is mostly evident only on 13 Ferury; however, it is lso present on 9 Ferury, ut with n orienttion 90 to the usul Bering-Frm strit line, moving rther from Greenlnd towrd Sieri. Ekrnn trnsport The Ekmn trnsports corresponding to the wind-stress fields of 5 Ferury nd 17 August re depicted in Figure 12. These trnsports re computed etween the surfce nd the 50 m depth level; the figures show the verge velocity in this lyer. On 5 Ferury (Fig. 12) we note series of lternting diverging nd converging regions over the Cndin Bsin, nd very intense divergence region under the strong tmospheric low ner Novy Zemly. The sitution on 17 August (Fig. 12) is dominted y huge divergence under the lrge cyclonic gyre, nd strong offshore trnsport west of Norwy, out 45 to the right of the southerly wind strem prlleling the Norwegin cost. The mximum velocities re out 8.6 nd 5.6 cm S l, respectively. Although not illustrted in this pper, res of strong divergence in the Ekmn trnsport tend to e indictive of res of ice divergence. This is prticulrly true for the cse of the lrge cyclonic gyre in the Cndin Bsin, indicting thinning of the ice cover. In some cses this cn led to res of ice opening s well s new ice formtion. 59

7 Wrn- Vrns nd others: Ic~ocen circultion in the Arctic WIND STRESS MAXIMUM STRESS = 0.56 NT/ M**2 WIND STRESS MAXIMUM STRESS = 0.52 NT/ M**2 ICE VELOCITIES CM/ SEC ICE VELOCITIES CM/ SEC Fig. 9. The wind stress () nd ice-drift motion () for 9 August Fig. 11. The wind stress () nd ice-drift motion () 17 August WIND STRESS MAXIMUM STRESS = 0.48 NT/ M**2 ICE VELOCITIES CM/ SEC 50 METER AVERAGE EKMAN TRANSPORT = 5.6 CM/ SEC Fig. 10. The wind stress () nd ice-drift motion () 13 August Fig. 12. The 1986 Ekmn trnsports: () trnsport jor 5 Ferury, () trnsport jor 17 August. 60 EKMAN TRANSPORT = 8.65 CM/ SEC

8 ROLE OF ICE COVER IN MOMENTUM TRANSFER To get feeling for this role, we hve simulted the winddriven rotropic currents with two kinds of forcing: the entire wind stress nd the ice-wter drg (under the ice). The results for Septemer re presented in Figure 13. The mximum velocities for the wind-stress cse re lrger thn the drg cse y fctor of two (4.5 versus 1.9 cm S I). The cyclonic gyres in the Beufort Se nd the Norwegin Se re out the sme, ut the two nticyclonic gyres, one ner Spitsergen nd the other 90 est on the sme ltitude, re stronger in the wind-stress cse. BA RO TRO PIC CIRCULAT10N WITH SEP 1986 IW ST RE SS B.~ R O TR OP 1 C C1RCl'L..l.: IO'-J WITH.::lEP AvERAGE WIND STRESS FOR SEPTEMBER-56 MA X1MUM STRESS= 0.17 NT/ M' '? CONCLUSIONS We hve mde numericl study of the Arctic ice cover nd upper ocen using 3-D coupled ice-ocen model. The model incorported turulent mixed-lyer model, nd ws forced with dily GGM-derived 12 h tmospheric fluxes. In prticulr, we exmined the momentum trnsfer nd circultion response to the trnsient winds nd het fluxes, nd mde n initil study of the synoptic nd sesonl vriilities of ice-drift motion, Ekmn trnsport nd rotropic currents. Preliminry exmintion of the model results reveled no significnt sesonl dependence of ice-drift response on the synoptic time scle, other thn lrger velocities with lrger wind stresses. Dily mximum ice-drift velocities rnge from 2G-40cms 1 in Ferury nd 15-30cms 1 in August. The corresponding men monthly mximum drifts were 11 nd 9 cm s l, respectively. In contrst, the rotropic response of the ocen is very different in the winter thn in the summer, with the ice cover plying much more importnt role in winter. The drg ssocited with the geostrophic currents, however, plys much igger role in the summer ecuse of the lighter tmospheric stresses. The well-known reversl of the normlly clockwise Beufort Gyre to cyclonic system in August tkes plce in few dys nd lsts well into Septemer. In Ferury, this gyre vries etween lrge, clockwise system covering ll the Cndin Bsin to smll, tight gyre centered over the southern Beufort Se. There is no evidence of ny reversl or even disppernce of the gyre in Ferury. The lrge divergence res seen in the Ekmn trnsport ptterns re importnt for ice formtion: in divergent res the ice will thin or open up nd refreezing will follow. Follow-on studies will exmine other months of 1986, s well s other yers of forcing. The model will e modified to employ prognostic ocen model with twowy coupling of the roclinic currents nd the computed density chnges, nd to include detiled correltions etween forcing, ice-drift motion nd ocen currents. ACKNOWLEDGEMENTS Fig. 13. The surfce-forced rotropic circultion for the month of Septemer 1986: () with ice-wter drg forcing (mximum velociry 1.9 cm {I), () with direct wind stress forcing (mximum velociry of 4.5 cm {I), (c) wind stress field. The uthors re gretly indeted to Ms Ruth Preller nd Ms Shelley Riedlinger of NOARL for mny helpful discussions concerning the Beufort Gyre reversl nd ocenic het flux computtions. Mny thnks re lso extended to the referees tht helped improve the pper sustntilly. This work ws funded y the Nvl Ocenogrphic nd Atmospheric Reserch Lortory under Progrm Element N. 6]

9 Wrn- Vrns nd others: Ic~ocen circultion in the Arctic REFERENCES Bjork, C A one-dimensionl time-dependent model for the verticl strtifiction of the upper Arctic Ocen. J. Phys. Ocenogr., 19, Clncy, R.M. nd K.D. Pollk A rel-time synoptic ocen therml nlysis/forecst system. Prog. Ocenogr., 12, Creegn, A A numericl investigtion of the circultion in the Norwegin Se. Tellus, 28 (5), Hiler, W.D., In A dynmic thermodynmic se ice model. J. Phys. Ocenogr., 9(4), Hiler, W.D., 111, nd K. Bryn A dignostic iceocen model. ]. Phys. Ocenogr., 17(7), Lemke, P A coupled one-dimensionl se ice-ocen model. ]. Geophys. Res., 92(CI2), 13,164-13,172. Levitus, S Climtologicl tls of the world ocen. NOAA Pro] Pp. 13. McPhee, M.C Se ice drg lws nd simple oundry lyer concepts, including ppliction to rpid melting. CRREL Rep McPhee, M.C Smll-scle processes. In Smith, W.O., Jr, ed. Polr ocenogrphy. Prt A. Physicl science. Sn Diego, CA, Acdemic Press, Mellor, C.L. nd L.H. Knth An ice-ocen coupled model. ]. Geophys. Res., 94(C8), 10,937-10,954. Mellor, C.L. nd T. Ymd A hierrchy of turulence closure models for plnetry oundry lyers. ]. Atmos. Sci., 31, Olers, DJ., M. Wenzel, nd]. Willernd The inference of North Atlntic circultion ptterns from climtologicl hydrogrphic dt. Rev. Geophys., 23, Peggion, C A method Jor determining solute velocities from hydrogrphic dt. L Spezi, SACLANT Reserch Centre. (Report SR-114.) Picsek, S., R. Allrd, nd A. Wrn-Vrns. In press. Studies of the Arctic ice cover nd upper ocen with coupled ice-ocen model. ]. Geophys. Res. Preller, R.H The NORDA/FNOC polr ice prediction system (PIPS)-Arctic: technicl description. NORDA Tech. Rep Preller, R.H. nd P.C. Posey A numericl model simultion of summe!' reversl of the Beufort gyre. Geophys. Res. Lett., 16(1), Semtner, A.]., Jr A numericl study of se ice nd ocen circultion in the Arctic. J. Phys. Ocenogr., 17(8), Svensson, U. nd A. Omstedt A mthemticl model of the ocen oundry lyer under drifting melting ice. J. Phys. Ocenogr., 20(2), Wlsh, ].E., W.D. Hiler, 111, nd B. Ross Numericl simultion of Northern Hemisphere se ice vriility, J. Geophys. Res., 90(C3), The ccurcy oj references in the text nd in this list is the responsiility of the uthors, to whom queries should e ddressed. 62