BGRvol2_p49HeatBalanceStudyonYalaGlacierinLanangHimalNepal
HirosiTKHARAKeijiHIGUCHIandDhrubaDasMULMI GgfrJEw′JYdJoJJJJ90
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Himalabout60kmnorthofKathmanduNepalThetopographyoftheglacierandthe SurrOundingareaisshowninFig1Theareaoftheglaciersurfaceisabout26km9The glaciericeowsftomthehighestpoint5700mtotheterminus5100minasouthwestward direction MicrometeorologicalobservationswerecarriedoutatthesitesshowninFig1byMP andBHMindicatesthemicrometeorologicalobservationsite5100montheglaciernear theterminuswithanaVerageinclinationof8degreesTheheatbalanceattheglaciersurface WaSObservedatthissiteatadistanceof70mmtheglaciericemarglninthedirectionof theprevai1ingwindPindicatesapointnearthe‘GlacierCamp’GCatthemoraine5090 atadistanceof30momtheglacierterminusThegroundsurfaceiscomposedmainly OfgneissBHindicatesthelowlevelobservationsite3920matthebottomofthewide Val1ey00rOftheLangtangRiver
andtbedensityorsnWWaSmearedasnovamplerTheoseryationsatsiteMw¢ madefbrtheperiodftomSeptember27toOctober28in1982Thetimesinthepresentr¢ poarestatedinNepalStandardTime ttIl′Ilj1ileIItl1Irr111illil111IiIlenlelilrltIi111prilturr tol6mlevelwasoccasionallymadewiththermistorsensorsAttheobservationsiteBH measurementofairtemperaturewasmadeataheightofaroundl5meveryhourbytheuse OfathermistorenSOrYamadaetal1984InadditionPreeipitationwascontinuously nlISuldby11iIllIIilalle
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insareaislovpre¢ipitationTbetotalprecipitationobse8datsiteBHwSabot00 m111jnSeptcnltlerbutilcreISeJhlboLItUnlminOe10heri111iLingthhL1ni11gl thepotmOnSOOnSeaSOnttheobservationsiteMattheglaeiermOStOftheprecipitation WaSduetosynopticscaledistutbancesandftllinthefbrmofsnowduringtheobservation p¢riodContrarytothisnearlyallprecipitationtookthefbrmofrainattheobservationsite T”lTllelemIinsuTrOUnIithtIILeiern→ithou†nLeOVelinSeptemberhuLocci Sio71a11ytherewasthinsnowcoveroflessthan20cmdinOetoberWhensynopticscale dirbancespassedthisarea lleCIoud1OllntOh→erCdalittl“uqJ…ilhiICnnVlJuLLt10ithedntimt
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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÷
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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
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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
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≠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
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NepalSeppyo4lSpeciallssue4217 RaoKSWngaardCandCot0R1974ThestruetureOfthetwodimensionalintemal boundarylayeroverasuddenehangeofsurfaeeroughnessJtmosSei3l738746
RiordanAJ198FoTmulationandtestingofacimatonomicsimulationorthemicroclimateof thedryvaeysandoftheLittleAmerieaV StationinAntarcieaBoundaryLayerMeteorol 295329

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