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49 HeatBalanceStudyonYalaGlacierinLanがangHimal,Nepal Hiros魚iTÅKÅHARA*,KeijiHIGUCHI*andDhrubaDasMULMI** G山ぐわわgfr〟JEw(-(〟血′J(す.Y岬dJ.ぐoJ汀「肋ー/わJJⅣ(J.90 *勒J〝属e∫瑠rCカ血∫′〟〟れ〃昭の′α乙加ルビr∫め′,極り,αイ甜 書*/ノ岬‘J川′町〟/り-・lJ川…て舟ど.l・、ハイー・ん川舟w(-1=JJ…、.n伽JハⅧJいご両ハ小人‘J//川仙仙k.\叩JJJ Abs什aぐt ObservationsortheJledt balanceat theglaciersurrheewerecarriedout during theearZy post- monsoollSeaSOnin198二neartheterminuso[YaTaGJa亡jerinLangtilngHimal、Nepal.Onlhebasis Ofresultsfrom7dayswithoutpassageofsynopticscaledisturbances,itisshownthatnetshortwave radiationprovided83㌔andsensibleheat月ux17チ∴respeCtivcly.ortheheatgaininthedaytime.Net longwaveradiationwasfoundtobealargeheatsink.Latentheat且uxmadenosignificantcontribu- tiontotheheatbalance.ThecoJltributionofsensibleheatfluxtothedailyheatgainwasgreatdespite thelowairtenlPerature(mean,一一3.9で).D亡tailed observationsrevealed that thestrongradiation inversionandtheresultantkatabaticwindplaymajorrolesintheenhancementofthelargesensible heat鮎Ⅹ.Itisalsoindicatedthatwarmairadvection鉦omthesnow-freeareainthedaytimehasa roleinmaintainingthelargesensibleheatnux,eSPeCialJyneartheglacierternlinus. 1.血血血血瓶用 Observationsoftheheatbalanceattheglaciersurfaceareimportantfbrunderstanding themassbalanceofglaciersandtkeclimatologicalandhydrolo由は1a甲∝tSOft鮎areas Wheretheglaciersare10Cated.Mostofthepreviousworksonheatexchangeattheglacier OrSnOWSⅦrねc8intbeNepalHima払yaIlaVebeenundertakenin仏esumermonsoon SeaSOninconneetionwiththestudyoftheablationprocess(InotleandYoshida,1980;Ohata andHigucbi,1980). Undercoolmeteorolo由calconditionsd∬ing血epost-mOnSOOnSeaSOntheablationof glacicrsisbelievedtobesmall・However,aSrePOrtedbyYasunari(1980),SnOW一正eeareas S㍍0ⅥndiI嗜癖acierscanaもsorもasubstantialpa頭oftheincomi喝radiation血etolow Surfhcealbedo,aCtingasaheatsourcefbrtheatmosphere.Thereislittleinfbrmationonthe 也emalin如enceorsuchsnow一触eareas℃pOntheprocessofbeattrans鈷rond征iers. Glacio-meteOrOlogicalobservations were attemptedinthelight ofthefbregoingftom Septembef27toOctober28血ringthepost-mOnSOOnSeaSOnin1982,neart壬IeterminⅥSOr Yala(Dakpatsen)Glacier,a$mallglacierinLangtangHimal,Nepal.Thepresentreport describestheobservationalresultsoftheheatbalanceattheglaciersurface,withspecial 扇tentiontot壬1e払ctorscontrollingtbesensibleheattransfbratthesllrね00andthee鮎ctof localwindsystem11POntheheatbalance. 2.OtISer一札tionsit¢S TheobservationswerecarriedoutatYalaGlacierinavalleyfacingsouth,inLangtang
OrSnOWSⅦrねc8intbeNepalHima払yaIlaVebeenundertakenin仏
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BGRvol2_p49HeatBalanceStudyonYalaGlacierinLanangHimalNepal
HirosiTKHARAKeijiHIGUCHIandDhrubaDasMULMI GgfrJEw′JYdJoJJJJ90
Je∫rC∫′′αr∫′α ‘J′lJ…lw1JJ…nJJ‘JkJJJ
Absat
Himalabout60kmnorthofKathmanduNepalThetopographyoftheglacierandthe
SurrOundingareaisshowninFig1Theareaoftheglaciersurfaceisabout26km9The
glaciericeowsftomthehighestpoint5700mtotheterminus5100minasouthwestward
direction
MicrometeorologicalobservationswerecarriedoutatthesitesshowninFig1byMP
andBHMindicatesthemicrometeorologicalobservationsite5100montheglaciernear
theterminuswithanaVerageinclinationof8degreesTheheatbalanceattheglaciersurface
WaSObservedatthissiteatadistanceof70mmtheglaciericemarglninthedirectionof
theprevai1ingwindPindicatesapointnearthe‘GlacierCamp’GCatthemoraine5090
atadistanceof30momtheglacierterminusThegroundsurfaceiscomposedmainly
OfgneissBHindicatesthelowlevelobservationsite3920matthebottomofthewide
Val1ey00rOftheLangtangRiver
andtbedensityorsnWWaSmearedasnovamplerTheoseryationsatsiteMw¢
madefbrtheperiodftomSeptember27toOctober28in1982Thetimesinthepresentr¢
poarestatedinNepalStandardTime
ttIl′Ilj1ileIItl1Irr111illil111IiIlenlelilrltIi111prilturr
tol6mlevelwasoccasionallymadewiththermistorsensorsAttheobservationsiteBH
measurementofairtemperaturewasmadeataheightofaroundl5meveryhourbytheuse
OfathermistorenSOrYamadaetal1984InadditionPreeipitationwascontinuously
nlISuldby11iIllIIilalle
ltrOlogiIlIditinSduriObilri
insareaislovpre¢ipitationTbetotalprecipitationobse8datsiteBHwSabot00
m111jnSeptcnltlerbutilcreISeJhlboLItUnlminOe10heri111iLingthhL1ni11gl
thepotmOnSOOnSeaSOnttheobservationsiteMattheglaeiermOStOftheprecipitation
WaSduetosynopticscaledistutbancesandftllinthefbrmofsnowduringtheobservation
p¢riodContrarytothisnearlyallprecipitationtookthefbrmofrainattheobservationsite
T”lTllelemIinsuTrOUnIithtIILeiern→ithou†nLeOVelinSeptemberhuLocci
Sio71a11ytherewasthinsnowcoveroflessthan20cmdinOetoberWhensynopticscale
dirbancespassedthisarea
lleCIoud1OllntOh→erCdalittl“uqJ…ilhiICnnVlJuLLt10ithedntimt
Th¢cioudamntOfmorenS710vassom¢SObservedtoeassociated¢
PaSSageOfsynopticsealedistlancesorthefbrmationoforogra‡icdoudsDeneOrO
0 5 0
10 10 15 20 25 25 5 SER OCT
Fig3Dai1ymeanairtemperatureSfromSeptember27toOctober23Opencircleshowsthedataat
SiteM5100mSOlidcircleatsiteBH3920m
basedonthedataffom2lobservationdaysThegeneralpatternOfthewinddirectionwas
nearlyalwaysomtheSSWinthedaytimeandfromtheNEwiththehighfiequenCyOf
morethan80atnighttimeSuchdirectionscorrespondtothoseoftheupslopeanddown
SlopewindsreSPeCtivelyTheupslopewindusuallystartedtoblowataroundO900andended
alittleaftersunsetSuchadiurnalvariationwaspronouncedonfinedaysSincethegeneral
WindwasweakduringtheobservationperiodSuChawindreglmeCanbeconsideredtoform
partofthemountainValleywindsystemdevelopedinthisarea
Fig4bindicatestheffequencydistributionof30minuteaverqgedspeedofprevailing
windsatl1mlevelatsiteMobtainedfromwholedayobservationson16daysWindspeed
WaSlessthan5mS1throughoutmostoftheobservationperiodwithameanvalueof31
mS‾1ItcanbeseeninFig4bthattheNEwindspeedismuchgreaterthanthatoftheS
SWwindthefbrmeris34mSrlandthelatter26mS‾10ntheaveragerespectivelyThe
greatwindspeedwasusuallyobservedintheearlymornlngOfafinedayduringthepost
monsoonseasonSincemaximumspeedwasobservedoftenataleveloflOtol5mabove
theglaciersurfacethiswindcanbeconsideredasaglacierwindinducedbythestrongcool
ingoftheairlayerneartheglaciersurfaceHoinkes19541955MunroandDavies1977
OhataandHiguchi1979DirenceinspeedbetweentheNEwindandtheSSWonewas
PrObablyduetothefactthatsuchakatabaticwindwassuperimposeduponthemountain
ValleywindWhichwasffomtheNE
O 1 2 3 5 6
U N ⊃ 0 ∝
0 2 3 4 5 6ms
Fig4TheffequencydistributionofwinddirectionandwindspeedatsiteMduringthepost
mOIISOOn SeaSOn
a3hourlywinddirectionbWindspeedorprevajlingwindsatllnllevel
aboveSSWwindbeIowNEwind
5Hee…taiersw¢ingpotmOnOnaSOI1
5lCal1ationoeatbalanc¢COmpOnentS
Theheatbalanceoft1eSrcelayerraaciercanbeexpressedasfb1lows
¢eeg¢e0 l
WhereQsisthenetshortwaveradiationQLthenetlongwaveradiationQHthesensibleheat
uxQEthelatentheatuxduetoevaporationorsublimatiorlQwtheheatusedtowarm
SnO7andiceoftiSW∝ayerandetheeattlSedtomeltsnovandiceFleStOWard
eadersurc8Wiiledenedaspositiveandtboseawaymthesw00aSnegae
HeattranSfbrbyprecipitationwasneglectedbecauseofitssmallamount
1Radiation
ThenetshortwaveradiationQswascalculatedfromtheglobalsolarradiationandthe
rectedsolarradiationmeaswedindependentlyTIenetlongweradiationCanbe
OainedasaresialneobseryedYalesregandlletradiationee
2SensibleandlatentheatxS
Consideringthethermalstratiationoftheairlayerneartheglaciersurfacetobestable
thesensibleandlatentheateSWereCalculatedbytheequations
54
152÷
βC8r kgJJ
ingtoftchcriteriaestablishedbyBradley1968andRaoetal1974Zlandzgweretaken
astheroughnessheightmean03cmandthelowestprolepointwithinaheightof40
CmreSPeCtivelyWherethetllrbulentheatCSWereCOnSideredtobeconstantwithheighL
ThisdsomitigateseectordiYergen∝arisingmtIeCbaraeristicprooat
baticwjnd
3Heatusedforwamingsurfacesnowandicelayerandmeltingsnowandice
InmostcasesthethicknessoftheoverlyingnOWCOVerOntheglaciericewas520cmnear
SiteMTheheatusedtowarmsnowandiceQwwascalculatedftomthetimevariationofthe
temperatleprO1eintlleSWcelayerdorntOadeptbor40cmaSSngthdensityortbe
gheierieeot05glenl‾IndtheCiliele11LorieeorO5cIl‾llglLhedensityot’
SnOWtheactualmeastredvaluewasused
TheheatusedinthemeltingprocessQMWaSeStimatedbythedirectmeasurementofthe
lowerlngOfthesnowsurfaceandthedensityofsnowThefteewatercontentwaslikelytobe
lessthanlOeveninthecaseofmeltingsnowSOitisnottakenintoaccounthere
SpeeddryandwetbulbtemperaturewereusedDaytime06001800heatbalanceatthe
glaciersurcewasobtainedfbrtheperiodsffom September29to
Octoberlandffom
October12to15DailybeatbalancewasestimateddtbeperiodomO600onOctober
i2toO600onOcOber16Whencompleter∝OrdswereobtainedAlltheotSerVatndays
Werepnmarilyaracteriz¢dbynewearconditionsandtIedevelopIntOrelocal
WindsystemIntheafternoonthesiteMwasoftencoveredwithorographiccloudshowever
SynOPticscaledisturbancesrarelycametOthisareaHencetheseperiodscanbeconsidered
asrepresentativeofthepostmOnSOOnSeaSOnTheglaciersurfhcenearthesiteMwascovered
Vitbsnow5J8cmindeptbbteOundneartbeglacierteminSVaSeeonsnow
Componentsofheatbalanceinedaytimearehovndiaamatic1yinFig5The
meanvalueOfcomponentsofheatbalaneeinthedaytimefbrthe7daysarcsummarized
inTableltOgetherwiththosevaluesofdailyheatbalancefbrtheperiodfromOctober12
to161tcanbeclearlyseeninFig5thatthcpredominantcomponentofheatgainisnet
S0WaVeradiationeWcIamOntStO83ortbeIleatgainonthera1lowed
QE ⊂ewt
Fig5Daytimeheatbalaneeattheglaciersurface
qnetlNiliali0etl“ler1′JihIekill11∫1illcnlIll
nuxQIrheatusedtowarmsnowandieeQNheatusedtonleltsnowandiee
ytes¢n1eheatfhxg17TbesuαaledoatmiddayraedmO65toO8
ThcnetIinoTltlSSOrIItCntheLLtnuiSmIlIilCeltLlrVapOrllreneIrthcnTue
ateglaciersw∝HeatlossbynetlongwaveradiationwasiaSinceradiation
fromthecloudswasmallduetolowdoudamountTherefbreheatgainbynetradiation
QNQsQLissmallmean66calCm‾aaCCOrdinglythesensibleheatfluxmean27
CalCm‾isatasignificantlevelThenegativevalueofQwrevealsthattheheatusedtowarm
tbesurα1ayerwiartba‡1heatreleaseetocoolingTes∝iayeriscooleddown
lltenCrentrblo“lutnightiLnLlmuIlhItiruirJtLr1iCil→lemlrItureL
00Cinth¢daytimeWhicbresultsinalowpercentageorheatavailablertmeltingproc¢SS
QMAsaresulttheaveragedailysnowmeltduringthese7dayswaslessthanO5cminwater
equivalentTheabsolutevalueoftheheatgainisnotsolargePreSumablybecauseofthe
reductionofincomngsolarradiationintheafternOOnWhentheorographiecIoudswere
medThegeneraltendenOreXCeSSiYatgaininreliontoeIeatlossn17
bepartiallyetol‡nderestimationorheatingintbescelayerSinceitwascalc1at¢d
ffomtemperatureat4dcpthsinthislayerbutnodatawereavailablebelowthedepthof40
Cm
TabelMeanvaluesofheatbalaneecomponentscacmattheglaeiersurfhee Mean
Mean
OL QTT QN heatgain heatoss e ¢ e Daytime balance 135 69 27 2 w54 20
162 145
9 ¶15 19 177 196 Dailybalane 131 153 46
DaytimebaJaneemeanValuesforSeptember29OctoberlardOctoberl15061800DailybaJanec
meanILLLSrUrOrl0l′1LInheItgIiilrnSenltSLHllIJllitiU1Lltll
meanheatTossttleSumOreaChnegaivecomponent
56
53Dailyheance
AsseeninTablellargeheatlossduetonetlongwaveradjationisthemostsignificant
54DirnalvariationormaincoInpOnentSOrheatbnce
InFig6atyPicalexampleofthediurnalvariationofnetradiationQNandsensibleheat
uxQHduringtheperiodOctober13060141800isshownbyho11rlymeanvaluesThe
LirlIreLtLunlltlnll7∴thLIitlthneOrIiltL11erIiureiIlthelirlU111ItL
theglaciersurfaceAZlthewindspeedatl1mlevelul1andthewinddirectionarealso
SbowinFig6eVaSne1y0121Cm‾min‾1ringalopedodatnigbtTbisis
areasonrtenegatiYeVaieOreindailybeatbalance‡ncontrasegvasalwaysposi
lYmin‾
∴
′ ′ γ ‰
6 2 18 0 6 12 18 0CT13 1
Fig6DailyeourseofmaineomponentsofheatbalaneeattheglaciersuTfaeeairtemperatureat
O8mevetemperatutedirencebet≠eenO8mlevelandtheglaeiersurfaeewindspeedatllm
levelandwinddirectionTheperiodswhensnowmeltoccurredarealsoshownSeetextfbrdetails
57
fIetofrmairdYeCIionfmmsrLnYfreerCaOnItLJ11PCmlureTrOtiTeaboICgladLLrSurlbce
epro£leorairtemperatreaboveeaciersrceisessentialrestimatingthe
SenSibleheatattheglaciersurfaceMorfactorsincontrollingtiletemPeratureprOAle
aretbecbangeorradiativeheatbalanceatesceandtbelocaladv∝tionSincethe
ObseryationsiteMisatadistanceoronly70momteglacieric¢minthete‡nperatre
procanbestronglyatrtctedbythewarmairadvectionfromthesnowffeeareaTreidl
19701eisman1977Riordan198Suchanedwassdiedbysimltaneousoserva
tionsonmeltingofnewlyfallensnowatsiteP30mawayomtheglaciericemafglnatthe
morailleairtemperareandsurcetemperareattIleSitesMandTheosemation
periodwasomOctober17to2l
T0ndwasemSnOWOnOctober17sno71locclredonOctober18lover
ingthesnowlinetotheelevationofabout4600mAfterthattheweatherrecoveredbutthe
SI10rCOVerremainedntilOctober21Considerabiecompactionortbesnowoccedon
October19ThewindswereSWnamelyomthegroundontotheglacierthrothoutthe
dtimeddngteobseationperiod
÷
2
‰ 912158 9 12 9 2518 9 12 OCT 19 20 21
Fig7EtOfwarmairadveetionfromthesnowfreeareaonlhetemperatureinerSionabovethe
glaciersurfaceatsiteMSnowfa1loccurredonOctober18
J7ltemperaturedireneebetweenO4mlevelandtheglaciersuTface
SurfacetemperatureOpenCircleSiteMSOlidcircleSiteP
dSnOWdepthatsiteP
lig7shWSWdcrllLlhurly11ueIrRICtempCriltur7atsitesMandP atld
teTllPtmlLltLtirenTlCte1Ol†llVelt71andthclrsuTRLCeie
4aisiteMiedm¢endrtnOWlIti0vithat
sastrongdendenOntIedirenceos¢etemperar¢nt‡l¢itesM andp
1‡drelhetbIITerilYltllCgrOundVaSinteliitl111CitLcJtlLmillimumtcmpcriLlurC
ofOCSd1neatdiren∝OrW¢tempeteneadndtbe
IltlUnrtti→ili‾iClt15IIsi≠’IllundwlVered
≠ithOWtlIrgCI11til1itlrCOl’sLlltllCemlertluleilducditInltStttJ
z0anddWaS00dtovithinlCOctoer19enSnOV00¢rbecamenine
lr1111nh1IlrtlndIhitl1pIeIllrrIeitllilju1ehr
lInSCtLCl111ilereliLbelIhcsnltheiLnJlhci”erLininRuIle…rthe
sensil17thnt1rrOnl111pLrildiLIlmeIrCiLlLolmgrclhtilltL75Iwund
l′ilSullIli1tISll11el∴JTl≠ltitl111Wllelltll…uIlls11iniCepelrdr
owedarapidincr¢aSeWiincrSingdirenceorswt∝eraresOctober21
Duringthisobservationperiodradiativ¢COOlingdidnotocetLreXCePtnearSunSetSOitwodd
beaSOm1tOCOnSideratadvectionplayedprlmaryrOleincontro11ingsllrαver
sionatsiteM Fig8owsticprosofirte¢reatMdpavi
CLCr≠illJeULlLtlhel1I11kJISn13mSJintlOtJllent1e”OW
econtiontllndsrcell300nOctoer17amarkedcontrastexisd
t“nltirteriltureIillirJltellhnlIllIel
ler11LlrJilTreiIthellrtOr11Ilnelle1l1ullee7eIeJ3∴≠’11Ull
th0ndwa00dvithsnowfl300nOctoitempera¢pltbotsites
resembledeachotherand7ldecreasedtoO8OC
SCbadireeCaneexplainedintb81iItOrairmaSmOdiation1nthesnow
conditionatsitePthereisadiscontinuityinsurfacetemperatureattheaciericemargin
andsbstantimodiationorairmasswilltakeplac¢eSpeCiallym¢artbeglacierswe
Vitllinl“ntlr11irttlLttCr01the1eritxIrinConrJl“nlherndi
eredilhn1JleIirlllIi11ItrleJilt11LliIitneerLtlIlUrRLetlIrCiIh
thLglllier→l1h…ill1li→nrli1Pertlur”LtuitiLliIlithtleunLlJi
“urtlleeItLIlheel1iIltcnpcrtturegmLlientiellr7rOinthetWtrPltrlrthc
0ndarylaeratSitespandM
SnOW†wlt SitP sJW⊂OVrtiitP
i∴∴ TEMPERATUREC
Figil†IirlCalsitSlCIliellIPcit Ontheground
1SnoOnditionSipOctori71l3tSn0dcditiatSite 10clerI1l
5
IltllelICirIl1Jetin“ittl1111lli11llhnleltlt1eIt
ksaSameanStOndtandmorecieaTiyereOnalheatrimentbeighHimal
Rekremces
HoirLkesH1955BeitragezurKenntnisdes
GletscherwindesArehMeteorGeophysBiokl SB6353
HolTlgrentiBensonCand
WellerG1975Ast11dyofthebreakupontheAreticsopeof
laskabygroundairandsatelliteobservalioJISCIimatcoftheAreticGeophysieallnstitute
UniversityofAIaska358366
‡noJandYosbidaM10Abnandheatebangeor8umGCierSeppyo
41Specia11ssue∴33
InoueandYasunariTt984SuTfaeeheatexehangeinthehighHimalayasTobepublished
MunroDSandDaviesJA1977Anexperimenalstudyoftheglacierboundarylayerover
metingieeJGlacioJogy1825136
OhataTandHiguchiK1979GravitywindonasnowpatchMctSocJapan57254263
OhataTandHiguchiK1980HeatbalancestudyonGlacierAXO10inShorongHimalEast
NepalSeppyo4lSpeciallssue4217
RaoKSWngaardCandCot0R1974ThestruetureOfthetwodimensionalintemal
boundarylayeroverasuddenehangeofsurfaeeroughnessJtmosSei3l738746
RiordanAJ198FoTmulationandtestingofacimatonomicsimulationorthemicroclimateof
thedryvaeysandoftheLittleAmerieaV
StationinAntarcieaBoundaryLayerMeteorol 295329
WebbtiK197tlIIrL11erehLtionshiIthelLgtinearrareilndcIenSionlostrongstuhiLit
quaJRoyM¢tSoc67⊥90
1eismanRN17SnowmdtatWOdimenionaltbulentdisionmodelWROW
R8S13337342
YamadaTMoOyamaHandTbapaK1Roieofi¢r1arindihomt
iatedwatersbedOfLangtgVali8yNepalHimaahtbisissue