Btま11et如ofGlaciologicalRes輯rCb18（2001）だトーJβ lii ⑥Japane父Soc呈etyofSnowand王ce Comparisonofmeteoro10gicarfeaturesinthedebris・freeanddebris－COVeredareasatKhumbuGlacierI NepalHimalayas，inthepremonsoonseason・1999 YukariTAKEUCHll，RijanBhaktaKAYASTHA：，Nozomu NAITO、，Tsutomu KADOTA andKaoruJZUMJ－ 1TheRe＄earChInstituteforHazardsinSnowyAreas，N軸ataUniversity，Niigata950仙2181Japan 2‡nst如もeぬrHy8rosp壬Ieric一札AtmospbericSciences，NagoyaUniversity，Nagoya464仙8601Japan 3Fron扇erObservatioIlalResearcbSystem払rGlめalC王Iange，ト18m16Hamamatsucbo，TokyolO5仙00ヱ3Japan （ReceivedJanllary24，2000；Revi駅dman11SCriptreceivedOctoberユ3，2800） Abstract Meteorologicaiobservationswerecarriedoutin也edebris一触eanddebris鵬COVeredareasofKbⅥmbuG主ac重er， NepalHimalayasfromMay22toJunel，1999．Comparまsonsofmeteorologicalfeaturesinthebothareaswere made．Therewaslittledifferenceofthenetradiationbetweenthebothareas．Thedistinctvalleywindcouldbe recognized．Tbeairtemperatureintbedebris｝COVeredarearⅣaSbigber仇anぬtint毎dめris一かeearea▼Tbe differencebecame＄mallinthedaytimebecausethevalleywindincreasedinthedaytimearldcoulddi独setheheat・ 1．lntroduction TllemOStpartOftheablこItionareaoflargeglaciersiI－ Himalayasiseoveredwithsupraglacialdt｝bris（Moribayashi and主iiguchi，1977；F房iiandH主guchi，19ア7）．王tisimportant， tberefore，tOunde柑tandtbetあeimaie鮪cもOfdebrislayeron meteorologyandablationrateindebris，COVeredarea，Many meteorologicalobservationswerecarriedoutandablation t：haracteristicsunderdebrislayerweTeShldied．foTeXこ1111ple lnouビandY（1Shida（198肌Naka＼＼▼OmldTakahashi（19ボ2）and Sakaig才α£（199乳However，nOSimuitaneousobservations ofmeteoroIogyinboththedebris－COVered andthedd）ris －fTeビareaSOnthビSameglaeierhavebeennladeLPriortothc presentstudy・Thispaperpresentsthemeteoroiogicalfea・ turビSObservedin the two areas ofKhumbu GlこICier．Ncpal Himalayas・Ablation，heatbi11；lnCeCharacteristicsandposi－ tおe degree－day facもOrS are repO珪ed by Kayastba g≠αg． （2000）andTakeucbig才α乙（2080）． Fig．1．Map of汰e Kbumもu Glacier，Nepa王Himalayas and observationsite＄．B：theobservationsiteonthedebris】イree bareice，D：theobservationsiteinthe（まel）ris－COVeredare乱 2．Observation methods M：払eobservations揉eく〉ntbelateraimoraine． Observationswereearriビd out arotlndtlleEverestI弓ase Camp（27p59′N，86051′E，5350ma．s．1．）ofKbumbuGlacier， re可児Ctively．Tbedif毎rencesinaitittldearesmali． which flowsfrom thebasin surroundedby Mt．Sa即1111atha Meteぐ■l■OIogiea】eLlements atldinstt．unlentSこIre Slml111ar－ （Everest，885針m）and王。hotse（8511m）．itisoneoft‡lelargest izedillTablel．Thesensorsof≠let and dr）：－bulb t円11pera・ glaciersinKムumbl汀egion，WiぬaleIlg仇ofabout17kmand tuT－eS＼＼・er亡・insertedindoublevinylchloridepipesforinsulat－ an area of abuut17．5krnコ（Watanabe（イ（ZI．，19錮）．The il－gSOlarradiatiollandvtLntilatELdb），microJans、Vithasolar obseⅣationperまodwa＄from May22toJunel，1999毎st batteryduringdaytime ateachobservation s主te．Most of before tbe monsoonseason． dヱ1t；l＼＼TereCOntinu（ruSl）▼reCOrded＼＼▼ithportabledataloggers・ ThreeobservationsitesB，DandMwereestablishedas MaintenanceofallinstrumentsatsitesB andDwasmade showninFig．1．Heatbalanceobservationsweremadeattheeveryday．lnthedebris叫freearea，ablationwasmeastlred debris－free（B）anddebr主s－COVered（D）areas，reSpeCtively． onceaぬyvi也sevenstak輩．Albedo（）ftbeicesuぬceat SiteM，Wberea主rtemperattlreWaSI℃eaSured，WaSぬesub＄id・ eacb stake was measured tw呈ce血ring払e observation iaryobseⅣationsiteplacedontbei離eralmorainecloseto periodataboⅥtll：00－12：000n鮎edays、王ntbedebris－COV｛ tbeglacierlⅥargirl．Tbedista‡1Cebetweens托esBandDis eredarea，ablationunderdebrislayerwasmeast汀edfour abo11t200m aparもand Misl．7km apartなom B．Tbe 【illleSaday（針OO，11：OO，1i：川〕and17：（10）こItartificiallrpI－叩ar－ altitudeofsitesB，DandMis5352m，5330mand5312m，edsiteswiththicknessofthedebrisiayerof2，5，10，20，30 ＊Presentaddress：NiigataExperimentalLaboratory，PublieWorksResearch王nstitute，Årai944一－0051Japan J6 BulletinofGlaciologicalResearch Tablel．Meteoro】ogicaleiemerltSandinstrumentsatsitesBandD． Site B：debris－freearea．SiteD：debrisCOVered area． Site Elements Instruments Recordinginterval B D Åirtemperature（dry－b111b） ○ ○ Tbemistorthermometer 30min． （1mhigil） くweトもulb） ⊂） ○ Tbermistort主IermOrneter 38min． 1Ⅳindspeed（1m，0．5mhigb） ○ ○ Three－CupanemOmeter 30min． Surfacetemperature ○ Infraredthermometer 30min． Globalradiation ○ 30min． A11wavenetradiation ○ Netradiometer 30min． Ablationamourlt ○ ○ OnceadayくB） F（〉urtim襟aday（D） Albedo ○ ○ AibedoIneter Twiceduringtheperiod（B） Fourtimesaday（D） and40cm，reSpeCtively．Tbesurねcetemperatureandalbedo ShowninFig．2b， of tbe debrislayerⅥFere aiso measured at those とi‡neS Tbe radiative balarlCe eqⅥation on theice or debds manually．Thesurfacetemperaturewerecontinuouslymea－ surfacescanbewrittenasfollows： suredatapointwith10cmdebrislayer，thethicknessof 5月十即＋A斤十m＝腫， （1） whichisnearlyequalto the mean thickness ofthe debri＄ 1ayeraroundsiteD．Moredetai1methodsofmeasurementat wherepositiveindicatestowardthesurface．SRisthesolar artificia11yprepareddebrislayerarereportedinKayas洩ag才 rad主atio‡l，忍だtbe re幻ected sbort－WaVe radiation，月度tbe α乙（2000）． atmosphericlongrwave radiation，7署the terrestriallong WaVeradiationandNHthenetradiation．SZ？onthedebris 3．ComparisonofmeteorologlCalparametersbetweenthe －COVeredice andNR onthe debris－freeiceweremeasured debrは－free and debris－COVerモd areas． directly．SRisconsideredto be the same atthebothsur－ faces．RRwasobtainedfromSHandalbedo，namely， 3．j．屋ね盛抜娩細 斤斤＝一一α5凡 （2） Albedos measured at seven stakes in the debris-free areawereshowninFig．2乱ThevaluesdecreasedonMay30 whereαisthealbedoofthebareiceorthedebrislayer．77？ ascomparedwiththoseonMay22atallstakesites．From was obtained by Stefan－Boltzmann’slaw，aSSuming the thisdata，thedailyalbedoofsiteB，Wherethemeteorologi－ Surfacesasblackbody．ARonthebareicecanbecalculated calmeasureIⅥentSWeremade，WaSObtainedbyinterpolating byequation（1）anditcanbethesamevalueonthedebris themeastlredva王tieSlinearly．Onthedebrislayer，a王bedowas layer．腫onthedebrislayerwasobtai‡1edl）yeqlほtion（1）． measuredeveryday．Themeanalbedoduringtheperiodwas Thevariationofsolarradiationduringtheobservation O．21．TheresultmeasuredonlOcmdebrislayeratll：00are periodis shownin Fig．3．It exceeded about1200Wm▼2 aroundnoononfinedays．Themeandailyvariationofthe four components of radiation and the net radiation were comparedbetweenbareiceandlOcmdebrislayerinFig．4， Thesearemeanvalueoffivefinedays（May22，25，26，30and 八 31）．The absolute value of RH waslarger on thebareice U ∧ U O n becauseofalittlehigheralbedo．Ontheotherhand，thatof V P 4 ¢ 3 777waslarger on the debrislayer，because ofthe higher 2 q （ 竜 U surfacetemperatllre．Astheresult，thenetradiationsinthe O （ U bo也areaswerealmostsa‡neaSSbowninFig，4（c）． 撃 （a）bareice F ▲ s托eEし」 5／22 5／30 1 2 ■ 0 － t 0 （ 0 ？ ∈ 邑 8 0 u 0 ▲ O 4 室 ．0 6 O P 3 0 P 庄 ¢ ▲0 一 ソ 4 0 q ー 眉 一 ∧ 〇 く U 0 一 2 0 O 8 O 0 0 0 5／22 5／2ヰ 5／26 5／28 5／30 6／l ∞5／225／235／245／255／265／275／285／295／さ05β16／1 Fig．3．Variation of solar radiation during the observation Fig，2．Albedoofthebareice（a）andthelOcmdebrislayerO））． period． Y．Takeucbiぞ才αg． プア 9 O （ 聞 （ U （ O 苧 O （ 0 N 6 ？ 0 ∈ ． ∈ 吉 ∈ 0 ∪ ミ 喜 0 。 リ じ 9 。 蔓 毒 膏 300 名 P 召 題 6 遥 還 ぷ 0 Z 3 －300 1－600 1 4 710131619 22 1 4 710131619 22 1 4 710131619 22 Loく；alTime Loca一丁ime Loca一丁ime Fig．4．Themeandailyvatiationofthefourcomponentsofradiationonthebare呈ce（a）and on払e18cmdebrisiayerくb〉，and汰enetradiatiorlOfthebotもareas（c）． ユユIl7ノブdや（1りJ（川‘7Jれ1ご（イ轟JJ direction froI11WeSt tO11Orth east did not oぐCurduringthe Thevariationsofwindspeedinthedebris－freeandthe observation period．Namely，a giacierwind which blows debris仙COVeredareasareshowninFig．5．Thewindspeed from the upglacier to the downglacier was not observed． wassmallgenerallyandeventhemaximumvalueduringthe Tbi＄SbouldbecausedtbattbeK‡1umblユGlacierisstlrrOund檜 periodwasabout2ms」∴狂wasra偽er重訂geinthedebris edbybigberri（短蔑eXCepモモhesotl払－WeStdirectionasseen －COVeredareathaninthedebris－freearea、Thereasoncarl inFig．1．Theprevailまngwind主sconsideredtobeavalley beconsideredtbatmanylCepinnac王esinthedebr主s一たeearea windTePOrtedfromearlier（Inotle．1976）．1tbloⅥ’Sfrし一mlo＼＼－er decreased thewind speed．Systematic daily fluctuation of toupperalongthevalleyduetotherisingofwarmedairin windspeedcanberecognizedinthebothareas，namelyit the daytime，Which causes the daily fluctuationinwind becamelargerinthedaytimeandverysmailintbenigbトSpeed． time．Especiallyintbedebrisイreearea，itⅥraSnearlyzeroin 払enigbttime．TbeⅥ㌢inddirectionconce訊けatedたomsout主I 3．ユAgrお汁ゆg和お柁 to sotlt壬IWeSt，Wbicbis from tbe doⅥⅥStream area Of the TlleVariatioTISOfairtemperこItl】reinthedebris－freLビarea Valley，bythe frequency of about60％（Fig．6）．Thewind （B），thedebris岬COVeredarea（D）andonthemoraine（M）are showninFig．7．Thedailymaximumairtemperaturesofthe 也ree sites were3．9，4．8and7，6℃in average during汰e period，ItwasthehighestatsiteMandtheiowestatsiteB． － 」 J O TbissbouldbecalユSedby払edif鎚rencesins㍑rfacetempera－ O ん （ tureofthesites，Thesurねcetemperatureofthedebris－free 2 ㌔ ∈ ） icewasO℃becauseofmeltingduringdaytime．Inthedebris P 。 －＜OVeredarea，thesurfacetemperaturedependsonthedebris 邑 s p thiekntlSS．Most of the ener紺absorbed on the thin debris u 妻 surface duringdaytime conduct toice arld me比it．Then， SurfaぐetビI11peraturビOfdel）lislayernl町belo＼＼▼ビrthanthat onthemoraine，wi1erethereisnoglaciericebelow．Onthe Otherhandinthenighttime，thedailyminimumairtempera・ 5／22 5／23 5／24 き／25 5／28 5／27 5／28 5／29 5／30 5／31 8パ tures oftbesite B，D and M were－1．9，－0．2arld1．5℃in F童g－5▲ Variationsofwindspeedin洩edebris◆fr綬anddd〉ris averageanditwasbigberatsiteD也antbatatM．Tbeair －COVered areas． temperattlredecreasedmoreslowlyatDcomparedwithatB alld M．This tendenc〉▼Can be seen every da）▼during the period． 0 （ U O ） 空 っ 葛 5 L 監 ∈ 芦 」 叩 く 5／22 5／23 5／24 5／25 5／26 5／27 5／28 5／29 5／aO 5／31 8ハ Fig．7，Variationsofairtempera餌rein血edebri＄イree，debris