Thermodynamic and Dynamic Ice Thickness Changes in the Canadian Arctic Archipelago in ...

24 Pages·2017·14.37 MB·English

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Thermodynamic and Dynamic Ice Thickness Changes in the
Canadian Arctic Archipelago in NEMO-LIM2 Numerical
Simulations
XianminHu1,JingfanSun1,+,TingOnChan1,++,andPaulG.Myers1
1DepartmentofEarthandAtmosphericSciences,UniversityofAlberta,Edmonton,T6G2E3,Canada
+summerinternfromZhejiangUniversity,38ZhedaRoad,Hangzhou,China,310027
++nowatSkytechSolutionsLtd.,Canada
Correspondenceto:XianminHu([email protected])
Abstract.SeaicethicknessevolutionwithintheCanadianArcticArchipelago(CAA)isofgreatinterest.Inthisstudy,based
on the NEMO numerical frame work including the LIM2 sea ice module, simulations at both 1/4 and 1/12 horizontal
◦ ◦
resolution were conducted from 2002 to 2016. The model captures well the general spatial distribution of ice thickness in
the CAA region, with very thick sea ice ( 4m and thicker) in the northern CAA, thick sea ice (2.5m to 3m) in the west-
∼
5 centralParryChannelandM’ClintockChannel,andthin(<2m)ice(inwintermonths)ontheeastsideofCAA(e.g.,eastern
ParryChannel,BaffinIslandscoast)andwaterchannelsinsouthernareas.Eventhoughtheconfigurationsstillhaveresolution
limitations in resolving the exact observation sites, simulated ice thickness compares well with weekly Environment and
ClimateChangeCanada(ECCC)NewIcethicknessProgramdataatnearbysitesexceptinthenorth.At1/4 to1/12 scale,
◦ ◦
modelresolutiondoesnotplayasignificantroleintheseaicesimulationexcepttoimprovelocaldynamicsbecauseofbetter
10 coastlinerepresentation.Seaicegrowthisdecomposedintothermodynamicanddynamic(includingallnon-thermodynamic
processesinthemodel)contributionstostudytheicethicknessevolution.Relativelysmallerthermodynamiccontributionto
icegrowthbetweenDecemberandthefollowingAprilisfoundinthethickandverythickiceregions,withlargercontributions
inthethinicecoveredregion.Waveletanalysisofthehourlysimulatedicefieldsclearlyshowsthethermodynamiccontribution
haveseasonalanddiurnalcycleswhileonlytheseasonalcycleissignificantforthetotalicethickness.Highfrequencychanges
15 arefoundinbothfieldsduringtheseaicemeltingandformationprocess,particularlyinthemeltingseason.
1 Introduction
The Canadian Arctic Archipelago (CAA), the complex network of shallow-water channels adjacent to the Arctic ice pack,
has been a scientific research hot spot for a long time. Scientifically, it is an important pathway delivering cold fresh Arctic
water downstream (e.g., PrinsenbergandHamilton, 2005; Mellingetal., 2008; Dicksonetal., 2007; Petersonetal., 2012),
20 that eventually feeds the North Atlantic Ocean, where the watermass formation and ocean dynamics play a key role in the
largescalemeridionaloverturingcirculation(MOC)andglobalclimatevariability(e.g.,Rheinetal.,2011;Hátúnetal.,2005;
Marshalletal.,2001;VellingaandWood,2002).Economically,underthecontextthatNorthernHemisphereseaicecoverhas
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been declining dramatically (e.g., Parkinsonetal., 1999; Serrezeetal., 2007; ParkinsonandCavalieri, 2008; Stroeveetal.,
2008;Comisoetal.,2008;ParkinsonandComiso,2013),especiallysince2007,shippingthroughtheCAA,viatheNorthwest
Passage(NWP),isofparticularinteresttocommercialtransportbetweenEuropeandAsiabecauseofthegreatdistancesavings
comparedtothecurrentroutethroughthePanamaCanal(e.g.,Howelletal.,2008;Pizzolatoetal.,2016,2014).Besidesthe
5 harshweatherandothersecurityissues(e.g.,icebergs),thebiggestconcernfortheopeningoftheNWPisstillthecondition
ofseaice,especiallyhighconcentrationsofthickmultiyearice(MYI)(Melling,2002;Howelletal.,2008;HaasandHowell,
2015).
Lietaeretal.(2008)estimatedabout10%ofthetotalNorthernHemisphereseaiceisstoredwithintheCAA.Seaicewithin
theCAAregionisacombinationofbothfirst-yearice(FYI)andMYI.MYIisbothlocallyformedandimportedfromtheArctic
10 Ocean,andnormallylocatedinthecentral-westParryChannelandthenorthernCAA(e.g.,Melling,2002;Howelletal.,2008,
2013). Since the late 1970s, the ice free season has extended by about one week per decade (Howelletal., 2009), with a
statistically significant decrease of 8.7% per decade in the September FYI cover. Reduction in the MYI cover is also found
(-6.4%perdecade)butnot“yetstatisticallysignificant”duetotheinflowofMYIfromtheArcticOceanmainlyviatheQueen
ElizabethIslands(QEI)gatesinAugusttoSeptember(Howelletal.,2009,2013).EventhoughtheArcticOceanicepackalso
15 extendstotheCAAregionthroughM‘ClureStrait,thenetseaicefluxissmallandusuallyleadstoanoutflowfromtheCAA
(Kwok,2006;Agnewetal.,2008;Howelletal.,2013).
Althoughthereisincreasingdemandforseaicethicknessinformationwithinthisregion,thereisstillverylimitedrecords
available(HaasandHowell,2015).Melling(2002)analyzeddrill-holedatameasuredinwintersduring1971–1980withinthe
SverdrupBasin(themarineareabetweenParryChannelandQEIgates,seeFig.1),andfoundseaiceinthisregionislandfast
20 (100%concentration)formorethanhalfoftheyear(fromOctober-NovembertolateJuly)withameanlatewinterthickness
of3.4m.Sub-regionalmeansoftheicethicknesscanreach5.5m,butverythickmultiyearicewasfoundtobelesscommon,
which is likely due to the melting caused by tidally enhanced oceanic heat flux in this region (Melling, 2002). The seasonal
export of the old ice from the Sverdrup Basin down to south was known in the past (Bailey, 1957), which helps to create
anothermajorregionwithsevereMYIconditionintheCAA,thecentralParryChannelandM’ClintockChannel(seeFig.1
25 forthelocation).Basedontwoairborneelectromagnetic(AEM)icethicknesssurveysconductedinMay2011andApril2015,
HaasandHowell(2015)estimatedtheicethicknesstobe2to3minthisregionwithMYIthickerthan3monaverage.This
supportsthegeneralspatialdistributionoficethicknesswithintheCAA,thickerinthenorthandrelativelythinnerinthesouth.
Observations were not only limited in time but also in spatial coverage, thus, numerical simulations are required to bet-
ter understand the ice distribution and variability in the CAA (e.g., Dumasetal., 2006; SouandFlato, 2009; HuandMyers,
30 2014).Dumasetal.(2006)evaluatedofthesimulatedicethicknessatCAAmeteorologicalstationsbutwithauncoupledone
dimensional(1D)seaicemodel(FlatoandBrown,1996).ThevariabilityandtrendsoflandfasticethicknesswithintheCAA
were systematically studied by a recent paper from Howelletal. (2016) based on historical records at observed sites (Cam-
bridgeBay,Resolute,EurekaandAlert)andnumericalmodelsimulationsoverthe1957–2014period.Theyfoundstatistically
significant thinning at the sites except at Resolute, and this downward trend is mostly associated with the changes in snow
35 depth. Although some of the numerical simulations used in Howelletal. (2016) produced a reasonable seasonal cycle, gen-
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erally,thesesimulationsoverestimatedicethicknessanddidnotdoagoodjobincapturingthetrend.Inaddition,thelackof
horizontalresolutioninthesemodelswerealsopointedoutinHowelletal.(2016).
Inthispaper,wewillfocusonthesimulatedCAAseaicethicknessoverrecentyears(2002–2016),andaddresstheskillofa
seaicemodel,includingbutnotlimitedtothosementionedinHowelletal.(2016).Tobemorespecific,thispaperwilldiscuss
5 1) the relative importance of thermodynamic and dynamic processes in sea ice growth/melting in simulating the possible
variability of sea ice and ocean surface fields in the CAA; 2) high frequency changes in ice growth/melting processes. This
paperstartswithabriefdescriptionofthenumericalsimulationsandobservationaldatausedinthisstudy.Thentheevaluation
of simulated ice thickness in the CAA region is presented in section 3.1. The spatial distribution and temporal evolution (at
selected sites) of thermodynamic and dynamic ice thickness change are discussed in section 3.2. Section 3.3 focuses on the
10 highfrequency(uptodiurnalcycle)variabilityinicegrowth/meltingprocesses.Concludingremarksandadiscussionaregiven
insection4.
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2 MethodandData
2.1 Numericalmodelsetup
In this study, the coupled ocean sea ice model, the Nucleus for European Modeling of the Ocean (NEMO, available at
https://www.nemo-ocean.eu)version3.4(MadecandtheNEMOteam,2008),isutilizedtoconductthenumericalsimulations.
5 The model domain covers the Arctic and the Northern Hemisphere Atlantic (ANHA) with two open boundaries, one close
to Bering Strait in the Pacific Ocean and the other one at 20 S across the Atlantic Ocean (Fig. 1, inset). The model mesh
◦
is extracted from the the global tripolar grid, ORCA (DrakkarGroup, 2007) with two different horizontal resolutions, 1/4
◦
(hereafterANHA4)and1/12 (hereafterANHA12).Thehighesthorizontalresolutionis 2kmforANHA12and 6kmfor
◦
∼ ∼
ANHA4inCoronationGulf–DeaseStraitregion,whichisneartheartificialpoleovernorthernCanada(Fig.1),andthelowest
10 resolution is 9km for ANHA12 and 28km for ANHA4 at the equator. In the vertical, there are 50 geopotential levels
∼ ∼
withhighresolutionfocusedintheupperocean.Layerthicknesssmoothlytransitionsfrom 1matsurface(22levelsforthe
∼
top100m)to458matthelastlevel.
TheseaicemoduleusedhereistheLouvainla-neauveIceModelVersion2(LIM2)withanelastic-viscous-plastic(EVP)rhe-
ology(HunkeandDukowicz,1997),includingboththermodynamicanddynamiccomponents(FichefetandMaqueda,1997).
15 Itisbasedonathree-layer(onesnowlayerandtwoicelayersofequalthickness)modelproposedbySemtnerJr(1976)with
twoicethicknesscategories(meanthicknessandopenwater).Theseaicemoduleiscoupledtotheoceanmoduleeverymodel
step.TheelastictimescaleistunedsmallenoughtodamptheelasticwaveintheEVPapproach(seeTable1),basedonthedis-
cussionsinHunkeandDukowicz(1997).Ano-slipboundaryconditionisappliedforseaiceinthesimulations,whichmeans
theicecanhavezerovelocityalongthecoast.However,itshouldbenotedthattheseaicemoduleusedinthisstudydoesnot
20 includearepresentationoflandfastice(e.g.,Lemieuxetal.,2016),whichmaynegativelyimpacttheseaicesimulationwhere
landfasticeexists.
Table1.Seaicemoduleparametersusedinoursimulations
parameter ANHA4 ANHA12
timestep(seconds) 1080 180
subsyclingiterations 150 120
timescaleofelasticwave(seconds) 320 60
Two simulations, ANHA4-CGRF and ANHA12-CGRF, are integrated from January 1st 2002 to December 31 2016. The
initialconditions,includingthreedimensional(3D)oceanfields(temperature,salinity,zonalvelocityandmeridionalvelocity)
as well as two dimensional (2D) sea surface height (SSH) and sea ice fields (concentration and thickness) are taken from
25 fromtheGlobalOceanReanalysisandSimulations(GLORYS2v3)producedbyMercatorOcean(Masinaetal.,2015).Open
boundaryconditions(temperature,salinityandhorizontaloceanvelocities)arederivedfromthemonthlyGLORYS2v3product
aswell.Atthesurface,themodelisdrivenwithhightemporal(hourly)andspatialresolution(33km)atmosphericforcingdata
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75oN 5.0
n
e a YLT/LT1 n d
c ti c O c e e nla
r r
A G
Q E I WEU 4.5
M
C
S
70oN
YRB
4.0
B
a
M n
B
C ay
C
YCB 3.5
65oN
YUX
YFB
3.0
YZS
60oN 9
8
7 H 2.5
u
d
s
6 o
n
B
a
5 y
4
2.0
100oW 90oW 80oW 70oW
Figure1.ANHA12(inset)modelmesh(every10thgridpoint)andhorizontalresolution(colours,unit:kilometers)intheCanadianArctic
Archipelago(QEI:QueenElizabethIslands;MCS:M‘ClureStrait;MCC:M’ClintockChannel)andHudsonBayregion(thickblackbox
highlightedintheinset).Notethecolourscaleisdifferentfromthatusedintheinset).Icethicknessobservationsites(seetable2forthe
details)areshownwithblackcirclesonthemap.
provided by Canadian Meteorological Centre (CMC) Global Deterministic Prediction System (GDPS) ReForecasts (CGRF)
dataset(Smithetal.,2014),including10mwind,2mairtemperatureandhumidity,downwellingandlongwaveradiationflux,
andtotalprecipitation.Inter-annualmonthly1 1 riverdischargedatafromDaietal.(2009)aswellasGreenlandmeltwater
◦ ◦
×
(5km 5km)providedbyBamberetal.(2012)iscarefully(volumeconserved)remappedontothemodelgrid.
×
5 WiththesamesettingasANHA4-CGRFbutdrivenwiththeinter-annualatmosphericforcingsfromtheCoordinatedOcean-
iceReferenceExperimentsversion2(CORE-II)(LargeandYeager,2009),anotherANHA4simulation,ANHA4-CORE,in-
tegratedfromJanuary1st2002toDecember312009,isalsoconductedtostudythesensitivityoftheseaicesimulationtothe
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atmosphericforcings.TheCORE-IIprovidesfieldsatvarioustemporalresolutions,a)6-hourly10-msurfacewind,10-mair
temperature and specific humidity; b) daily downward longwave and shortwave radiation; c) monthly total precipitation and
snowfall.
Notemperatureorsalinityrestoringisappliedinanyofthesimulationsusedinthisstudy.Withoutsuchconstrainsthemodel
5 evolvesfreelyintimetohelpunderstandbetterthelimitationsofthephysicalprocessesrepresentedbythemodel.
Monthly ice thickness at 1/4 resolution from the GLORYS2v3 product with sea ice assimilation is also utilized in this
◦
studytobetterunderstandtheinitialconditionissue.
2.2 EnvironmentandClimateChangeCanadaNewArcticIceThicknessProgram
Toevaluatetheperformanceofthemodelintermsoficethickness,simulatedicethicknessiscomparedtotheobserveddata
10 from Environment and Climate Change Canada (ECCC) New Icethickness Program (hereafter ECCC thickness). The new
ECCC thickness program, the second stage of the Original Ice Thickness Program Collection used in Dumasetal. (2006),
startedinthefallof2002,andcontinuedtothepresentatonly11stations(includingsitesinlakes).Measurementswerecon-
ductedweeklyatapproximatelythesamelocationclosetoshorebetweenfreeze-upandbreak-upperiod(whentheicewassafe
towalkon)withaspecialaugerkitorahotwireicethicknessgauge.DataismadeavailabletothepublicbyEnvironmentand
15 ClimateChangeCanadaundertheOpenGovernmentLicense(Canada)onhttp://open.canada.ca/data/en/dataset.Eightcoastal
sites,CarolHarbour(YZS),HallBeach(YUX),Iqaluit(YFB),CambridgeBay(YCB),Resolute(YRB),Eureka(WEU),Alert
YLT(YLT)andAlertLT1(LT1),wereusedinthisstudy.ThedetailedlocationinformationofeachsitecanbefoundinFig.1
andTable2.
Table2.ECCCicethicknessstationlocations(onlysitesusedinthisstudy)
site longitude latitude
CarolHarbour(YZS) 83.153◦W 64.130◦N
HallBeach(YUX) 81.230◦W 68.780◦N
Iqaluit(YFB) 68.517◦W 63.726◦N
CambridgeBay(YCB) 105.06◦W 69.113◦N
ResoluteBay(YRB) 94.884◦W 74.684◦N
Eureka(WEU) 85.942◦W 79.986◦N
AlertLT1(LT1) 62.593◦W 82.602◦N
AlertYLT(YLT) 62.420◦W 82.753◦N
Unlikethe1DmodelusedinDumasetal.(2006),whichcanbeappliedattheexactlocationwherethemeasurementswere
20 carried out, three dimensional (3D) models usually have horizontal resolution issues in resolving the observation sites, even
with the high resolution ANHA12 configuration used in this study. Interpolation is needed to do the comparison between
simulated fields and observations. This is also mentioned in Howelletal. (2016). To interpolate simulated fields onto the
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nearest water point (x ,y ) of each observation site (x ,y ), we utilized a modified inverse distance weighting (IDW)
k k obs obs
method(eq.(1))proposedbyRenka(1988):
R d
f = [ w− k]2 (1a)
i
R d
w k
f
i
w = (1b)
i N f
i=1 i
N
P
5 Qtarget = Qiwi (1c)
i=1
X
whereR istheinfluenceradiusaboutpoint(x ,y ),d isthedistancefrompoint(x ,y )toeachneighboringpoint(x ,y ),
w k k k k k i i
f istheinversedistancefunction,w istheweightfunctiononeachneighboringpoint(x ,y ),N isthenumberofneighboring
i i i i
pointswithinR ,Q isvariablevalueoneachneighboringpointandQ isthefinalresult.Inpractice,nineneighboring
w i target
points,includingpoint(x ,y ),wereconsideredinthecalculated.AsR issettothemaximumvalueofd andlandpoints
k k w k
10 shouldbeexcluded,eventuallyuptoeighteffectivepointsareusedinourinterpolationprocess.
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3 Results
Inthissection,first,theicethicknessreproductionabilitywithintheCAAoftheNEMOLIM2configurationsusedinthisstudy
will be examined via comparisons with the ECCC thickness. Then the detailed thermodynamic and dynamic ice thickness
changes,boththespatialdistributionandtemporalevolutionatselectsites(CambridgeBayandResoluteBay),basedonthe
5 simulation outputs willbepresented. Then, thehigh frequency ice growth/melting processes resolved by thesimulation will
bestudied.
3.1 Icethicknesscomparison
Figure 2 shows the ice thickness comparison with observations. In general, both ANHA4-CGRF (blue lines) and ANHA12-
CGRF(redlines)simulationsproducesimilarseasonalandinter-annualvariationsinicethickness,whichcomparereasonably
10 well at some sites (i.e., YCB, YZS, YUX, YRB,YFB) but not at the rest (WEU, YLT, LT1). Although the observations are
missingintheseaicemeltingseason,anasymmetricseasonalcycle(ashorterfastermeltingperiodfollowsarelativelylonger
slow growth period), is evidenced by the available data, and reproduced by the simulations. Taking account of the model
resolution,theinterpolatedsimulatedicethicknessreflectsactuallythevariabilitysomedistanceoffthecoastratherthanthe
exactobservationlocations.Thegeographiclocationdifferences,whichisalsorelatedtomodelresolution,couldalsoleadto
15 discrepanciesinthecomparisonshere.Thus,ifthemodelcancapturetheseasonalcycle(e.g.,multipledatapointsinbothice
growthandmeltingseasons),themodelislikelycapableofsimulatingtheprocess.
AtYFB,themodeldoesagoodjobinmostyearsbutfailedtocatchtheverythickseaicein2014,2015and2016(Fig.2h).
Thiscouldbealocalatmosphericforcingfieldbias,oramodelresolutionissue,i.e.,themeasurementscapturedverylocalized
extremesbeyondtheabilityofmodeltoresolve.SimilarbehaviorhappensatYZS,YUX.Furtherinvestigationisneeded.
20 AtWEU,YLTandLT1sites(Fig.2e,f,andg),thereisaclearinitialvalueissue( 2matYLT/LT1and 1matMEU)that
∼ ∼
leadstotoothickseaiceinthesimulations.NotethatneitherANHA4orANHA12hasthecapabilitytoresolvethedifference
between YLT and LT1, thus, the same simulated values are shown on the figure for both YLT and LT1. At YLT/LT1, both
ANHA4-CGRF (blue line) and ANHA12-CGRF (red line) show similar inter-annual trends to that in GLORYS2v3 (which
extends back to 1993, greenline), meaning it is likely a pure initial value problem rather than the model equilibrium issue
25 mentioned in Howelletal. (2016). In addition, the seasonal cycle is not clear in the GLORYS2v3 product. The issue is also
presentinsomeyears,i.e.,2005–2007,intheANHA4-CGRFandANHA12-CGRFsimulations.ANHA4-CORE(orangeline)
isgenerallyimprovedcomparedwiththeobservationsinboththeamplitudeandseasonalcycle.However,thisimprovement
wasachievedbyaccident,andisrelatedtoasnowdepthissueinthissimulation(moredetailswillbeinthediscussionsession).
Thus,itdoesnotindicatethatCORE-IIforcingisperformingbetterthanotheratmosphericforcingdatasetsinthisregion.The
30 equilibriumissue,i.e.,icethicknesskeepincreasing,mighthappenatWEUinoursimulationswitheitherCGRForCORE-II
forcing.Theupwardtrendover2005to2007isalsopresentintheobservationsbutismissingintheGLORYS2v3although
GLORYS2v3hasasmallthickness(whichislikelyduetodataassimilationoranatmosphericforcingissuein2005).Itstrend
doesnotreflecttherealchange/variability
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(e)
2.5 6.0 LT1
5.0
2.0
1.5 4.0
1.0 3.0
0.5 2.0
0.0 1.0
(a) YRB
(f)
2.0 6.0
YLT
5.0
1.5
4.0
1.0
3.0
0.5
2.0
0.0 1.0
(b) YCB
(g)
2.0 5.0 WEU
1.5 4.0
1.0 3.0
0.5 2.0
0.0 1.0
(c) YUX
(h)
1.5 1.5
1.0 1.0
0.5 0.5
0.0 0.0
(d) YZS YFB
04 06 08 10 12 14 16 04 06 08 10 12 14 16
Figure2.SimulatedicethicknessateachselectedECCCthicknesssite(figure1andtable2,unit:meters)fromJanuary2003toDecember
2016(orange:ANHA4-COREsimulation;green:GLORYS2v3product;blue:ANHA4-CGRFsimulation;red:ANHA12-CGRFsimulation)
againstweeklyECCCobservations(blackdots).NotetheGLORYS2v3productisamonthlymeanfieldwhiletherestofthesimulationsuse
5-dayaverages.
At YCB, simulations (red and blue lines in Fig. 2b) with CGRF forcing show very good agreement with the observations
exceptduringthewintersof2013and2014.Consideringthehorizontalresolutionofoursimulationsisnotcapableofresolving
theinnerbayattheCambridgeBay,thematchinicethicknessbetweenthesimulationandobservationsindicatesthevariation
oficethicknesswithintheinnerBaymightbesmall.BothANHA4-COREandGLORYS2v3simulationsunderestimatedthe
5 maximum values in winters by 0.5m. This indicates CGRF forcings might provide more realistic surface inputs in this
∼
region.
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AtYRB,itismorecomplicated(Fig.2a).Priortothesignificantseaicemeltingin2007,noneofthesimulationsshowice
free conditions in this region in summer. GLORYS2v3 shows relatively thinner ice in summer months but it is still 0.5m to
1.5mthick.Itcouldbetheinitialvalueproblem.However,highfrequentlyvariationseveninwinterintheANHAsimulations
suggest that the ice growth process is not dominated by a smoothly changing physical process (e.g., air temperature). Thus,
5 itislikelyduetothephysicalprocess(e.g.,advectionfromsurroundingareas).Thiswillbediscussedmoreinthefollowing
section.Post2007,theseasonalcycleintheseaicefieldismoredistinct,althoughicefreesummerconditionsdonothappen
everyyear.After2010,simulationsproducewinterseaicethicknessmuchclosetotheobservations.
3.2 Thermodynamicanddynamicicethicknesschange
In the real world, both the thermodynamic and dynamic ice thickness processes are coupled together (occurring at the same
10 time).However,withtheassistanceofnumericalmodel,thetwoprocessescanbedecoupled(showninequation(2))tobetter
understandtherelativeimportanceofeachprocess.
∆H = ∆H +∆H (2)
total thermal dynamic
where ∆H is the total ice thickness change over a specific time interval; ∆H is the ice thickness change due
total thermal
toverticalheatfluxes(throughtheatmosphere-ice-oceaninterfaces);∆H istheicethicknesschangeduetodynamic
dynamic
15 processes.Inpractice,asimpleapproachisutilizedtocomputethetwotermsontherightside.∆Hthermaliscalculatedbased
onthemodelthermaliceproduction.∆H istakenastheresidualfromthe∆H .
dynamic total
3.2.1 Spatialdistribution
HerewefocusonicegrowthprocessbetweenDecemberandAprilofthefollowingyear.Figure3aand3bshowthesimulated
ice thickness in ANHA12 at the beginning of December and at the end of April, respectively. Geographically, at the end of
20 April,a)verythickseaiceislocatedinthenorthernCAA( 4mbytheendofApril)withregionalmaximum(> 4.5m)at
∼
theopeningstotheArcticOcean.b)lessthickseaicecoverswestern,andcentralParryChannel(justabovethesiteYRB)and
M’Clintock Channel with a thickness of 2.5m to 3m. c) relatively thin ice (<2m) is mainly in the southern CAA, eastern
Parry Channel, coasts of Baffin Islands and within Hudson Bay. Invasion of the Arctic Ocean ice pack through the northern
CAAopeningsandtheadvectionfromthereintocentralParryChannelareclearlyshowninthefigures,consistedwithprevious
25 studies(e.g.,Melling,2002;Howelletal.,2008;HaasandHowell,2015).
During the winter, sea ice grows everywhere in the CAA regions due to the thermodynamic cooling (Fig. 3c). But the
totalincreaseoverthewinterisnotevenlydistributedinspace.Norisicegrowthlargestinthenorth.Largethermodynamic
ice growth is seen in the eastern CAA (eastern Parry Channel, Nares Strait, Baffin Island coast and western Hudson Bay),
Amundsen Bay and many coastal regions (e.g., western coast of Banks Island, northern coast of western Parry Channel).
30 Regions covered by thick sea ice (i.e., the northern CAA, west-central Parry Channel and M’Clintock Channel) show less
thermodynamicicegrowthoverthewinter.ThisisparticularlytrueinthenorthernCAA,likelyduetotheexistenceofalready
thickicereducingtheheatexchangebetweentheoceanandatmosphere.
10