Bulletin ofGlacierRe＄earCh12（1994）25−30

乏5◎DataCenterforGiacierResearc王】，JapaneseSocietyofSnowa‡1dIce

Seasonalchangeofthetroposphereintheearlysummerof19930VerCentralTibetobservedin theTangguJa mountains
Nobuhiko ENDO．Kenich UENO and Tetsuzo YASUNARJ

InstituteofGeoscience，UniversityofTsukuba，Tsukuba305Japan（ReceivedApri115，1994；RevisedmanuscriptrcceivedJuly23，1994）

Abstract

Aerologicalobservationswerecarried out from MaytoJuly of1993to study thecharlgeirl

atmosphericconditionswiththeseasonalmarchintheTanggula mountains（33．OON，92．OOE）inthe
centralTibetan Plateau．

Dur主ngthisperiod，increasesintropospherictemperattlreandspecifichtimiditywereabout5K
andabout3gkg▼1，reSpeCtively．Shorトperiodfluctuations（withabout5daysperiod）inallupper−air
meteoroiogicalelemerl短WeredominarltintIlepre−mOnSOOnSeaSOn，Whereaslargeamplitt王de，iov−frequencyosci11ationsofabout15Fdayperiodwereprominentduringthemonsoonseason．Abrupt

ChangeofthevariationpatternoccurredaroundJunelO．

ThediurnalvariationofthePBL（planetaryboundarylayer）wasexaminedunderfairweather
COnditionduringthepre−mOnSOOnSeaSOn，Amixed1ayerwithalmostuniformpotentialtemperature
VaSObservedwithmaximumheightofaround7000仙8000m，andverticalまyl王niねrmdistributionof
moistureis also noticeableinthe afternoon．

1．lntroductjon

Manyobservationalstudiesandnumericalstudies

Plateau．Yeh and Gao（1979）first described偽at

remarkablediurnalvariationinvariousmeteorologiT
Calelementsovertheplateauanditsvicinity，Yanai

bavesuggestedthattbetbermaie鮪ctoftheTibetan andLi（19銅）sttldiedthestructureofthePBLoverthe
plateauplaysanimportantroleinthe onset andthe
plateau，relating to the atmospheric heating．They
maintenance ofÅsian sllmmer mOnSOOnそHalln andObservedadeepaIldweま1mixedlayerovertheⅥreSt−Manabe，1975；LuoandYanai，1983，1984；Heetal．，
ern and centralplateau at1200UTC．They also
1987；Yanaig≠αg．，1992〉．Nitta（1983），uSingtheFirst
notedthattbemoistureisnotwellmixedverticalまy．
GARP（GlobalAtmospheric Research Program）
However，the diurnalvariation of the PBL de・
GlobalExperiment（FGGE＝evelIl−b data，found a SCribed so far based on twice−daily data，ind厄dinglarge diurnalvariationin tropospheric heating andFGGE and QXPMEX data．There had been nothat the therma11yinducedverticalcirculationhas apronounceddiurnalcomponent．Theyalsonotedthat
the Tibetan Plateau acts as aheat sourceinspring

be solved．

moisturesink Yanaiet al．（1992），uSingFGGE and upper−air observations to fully describe the diurnal
the Cbinese QinghaiⅩizang Plateau Meteorology
Variat主on of PBL over the Platealユ．TIle reiation
Experimentin1979（QXPMEX79）data，analyzedthebetweenthe changesinsurface fluxesvariation andiarge−SCale fie払verticalcircuiation．Tbey foundtimeevolutionoftbetroposphereisaまsoaqlユeStiontoand summer．

Theplanetaryboundarylayer（PBL）withlarge山

amplitude diurnalvariationis suggested to play animportant roiein血e beating汀1eChanism over tbe

IntensiveaerologicalobservationswerecorldtlCtT
edinearlysummerintheTanggulaMountainsintheCentralpartoftheTibetanPlateau．TheaimsoftheObservationswerel）toinvestigatethediurnaivaria−
tionandverticalstructureofthePBL，2）todescribe
tbeseasona王cbangeoftbePBLaIldtbevertica王struc−BulleとirlOfGlacier Research

ご iture of払e tropospbere relati11g tO the onset（〉f tbemonsoon，and3）to clarify the characteristics ofthe

disturbanceswhichcauseprecipitationontheplateau．

Tbesl汀facemeteoroioglCaleiemenもSWereObser−

ved to evaluate the surface lluxes at the launch site

fromMay21to September21，1993．Table2shows
Int九重sreportwepresentsornepreliminaryresl鵡sthelist ofinstruments，
ontheseasona王evoiutionarldthediurnalvariationof
Rad主osonde wasroutineiy重atinC壬1ed at O880BST
払everticalstructureof也etropospbereandtbe壬〉B王J（00OOUTC）every day．‡ntensive observations wereCarriedoutぎor32daystoobservetIleVariationoft壬1e
fromthedrypre−mOnSOOnSeaSOntOtheⅥrettermOn−

SOOrlSeaSOnintheTanggulaMountains．
2．Observations

WetlSe（まBeijing Stan血rd Time（BST，UTじ十8hot汀S）int‡1isreport．Theiocaitimeoftheobservかtion areais approximately 2 hours behind BST，
Aerologicalsoundings were madein the TanggulaVerticalstructureofthePBLwithlaunchingevery6

hours from O800BST（0000UTC）to 2000BSTく1280UTC）．Specia王01）SerVationswerealsotakenfor
3−daysもOintensivelyobservethediurnaivariationof
the verticalstructure of払e P8L withlaunc主Iing ofradiosondesevery3わoursfromO800BST縛仲軋汀C）tothenextO800BST（0000UTC）．

Mountains（33．0わN，92．0らE，5070ma▲S．主．）in払ecentrai 3．SeasonaIev01ution oftheverticafstructureofthe
Tibetanplateautota呈1y200timesfromMay2（）toAug
tropospherefromthepreLmOnSOOnSeaSOntOthel，1993，Tbetypeofradioso‡1deistypeRS80−ま5Nof
mOnS00nSeaSOn
VaisalaCo．Ltd．，Which measurespressure，tempera−ture andrelativehumiditywithhighverticalresolu・Figurelashowsatime−heightcrosssectionofthe
冒on（every2seconds），Wi仏紙eOMEGAnavaidsys−
ZOnalwindfromtbesurface（507針ma．s．りto20kmat
tem for measuring wind speed arld direction（seeO800BSTく0000UTC）．Tわestro喝Ⅶ彷teriies（王argerTablel）．
than30ms¶ま）wereobservedintheuppertroposphere
く12岬15k王n）until洩emiddieofJune，Whiletわewester−
Tablel．L主st ofinstrumentsusedforrad主osondeobserva−

1ieswereweakenedafterthemiddleofJune（lessthantion

Typeofreceiver
TypeofsondeWindfinding

油as血喝raT聯擁SO霊感on

PressureTemperature
Humidity
WindSpeed笥rind Dire（：t主onl哲avelengtb
Weightoぎballoon

MlVll（VaisalaCoりLtd）
RS80▼15N（VaisalaCo，，Ltd）
OMEGÅNavai（まWindfind壬ng
lO60to3hPa／0，1hPa＋60to叩900C／0．10C
OtolOO％RH／1％RH
Oto180ms−1／仇1ms▼1
1to3600／lO
4（）3MHz250g

20ms皿1）．Aweakeasterlywindappearedsometime
intheまowestlO80mlayer．Tbelargeamplitlユdeof
t壬IeZOnalwindfiuctⅥationisobservedⅥrithaperiodof
around5daysinthel叩pertrOpOSpherebeforeJune15，
Wbiie the fまuctuation of tbis period rarlge WaS nOtClearwithrelativelysmallamplitudeafterJune15．

Figurelbshowsatime山heightcrosssectionofthemeri（まionaまwi王ュd．Nortぬeriywasdo王Ⅵinantabove15

km during the observationa重period．ⅠもSeemS tbat
SOutllerly and‡10rtberly alternatively appeared with

Table2．ListofsurfacemcteorologlCalinstrumentsatBaseCamp．
Ele汀まentS

Sensor

AccⅥraCyMan血如er

Air Temperature

PlatinlimreSistor
0．1￠C VaisaiaCoっLtd．
（forcedventilatedsbel短rラ0．2℃ C封甘NOCo．，Ltd．
Humidi†r
Hygroscopicmacromolec11iarrnateriai 1％R壬iVaisaiaCo．，Ltd，
2％RIiCHINOCo．，Ltd．
Windspeed
3仙CupanemOmeter
0．1ms．1MakinoCo．
1町ind（】irect主onPote王1tiometertype
20
VectorInstrumeIltS
G王obaまsolarradiaとion
3％
EkoCo．，Ltd，
Temperatl汀ediffererlCetype3％
EkoCo．，Ltd．
Refiectivesolarradiat童0‡l Temperaturedifferencetype
Netradiatiく椚
3％
Ca‡叩be11Scie‡ltific，inc．
Temperatio主Idifferencetype
Grolエndsurfacetemperattire Infraredra（iiometer
0．5％ EverestInterscience王nc．
Groundtemperature

GrolユndbeatfllユⅩ（8ノノm−14〟m）

Thermister
Temperaturedi抒erencetype

0．10C
5％

Grant
EkoCo．，Ltd．

27

Erldし〕（TJ．JJ．

∪−Wind（m／ s）

periodoぎabolユも5daysぬro喝h軌etroposphereu‡lder

15kmbeforeJune21・Å托er京王ne21，5no油erまydays

andlO southerl）・daysseem to have appeared aIter一11tivel）▼illthelayerbビtⅥでen8alld15kTll，＼Vhi）einthe

iayer be紬een the suぬce and 8 km northerly

prevailedthroughtheperiod．Theamplitudeofthe
meridio‡1aiwi‡ユdfl㍊Ct㍑at主onbeぬreJune21wasla曙er
tha11tllatafterJune21．

The timerheight cross se・Ction of the potential
temperature主sshowninFig・1c，T主1etrOpOpau既WaS
locatedataround13kmattbeendofMay．hJune，
thetropopauseheight wasこIbmpt】）T r；lisedto arotlnd
17km・Th主s払eigbtcontinueduntil七重Ieendoりuまy．
ThisabruPtShiftofthetropopausemayberelatedtし）the migratioT10f the SouthJIsian anticycIoneL，1（TibetanIligb）鉦omIndochina（Fig．2）サH▲†」

遡塑上…＿▼＿，＿【「＿▼．ゝJ肌＿⊥

PolenlialTemp．（K）

∴・∴
嘗︸
芸潜￠
ぷいN
∴
∵ 」塾町，1＿＿．．＿」些哩＿＿．、＿⊥ 【【．姓、】岬」
・SpesificHumidity（0・lg！kg）

ニml
l頸X碍
●耶tT〔吼）1引X時う㈹．＿．．．、】榊−3㈲0、

診1200Oq〉11∝愉エ†∝泊89￠088￠錐ア￠0￠甜小）禦）00

F料1＿（a）■l、i111ellビigh亡Sビ亡【it）Tla100Z rし＝■Zてn；ll≠，ind（nls一：）．ぐいIll（l＝￣ 山一ビl・＼√ユ1is5！11Sl．＼ aIu（、S TllOlでtha【lコいTllS1at￣ehこIt（、h（Xlこ＼・alしIeさIes＄thilJlけnlS一口l・ビSllad（d．
tb）ThこIfformビri〔1i川1al＼＼，ind＝1Sr［）．CoTlt■）uri11ter＼∫alk§ms爪1and posit紬e valu農are Sbaded。（c）Tbaモforpote王Itia王 temperature 終〉、S￠lid triangles aretropopause．1dlThat for sl）eCifit：humid巾：り什1gkg−り、Fiき：．？・5−dal・nleこⅢgビ叩いt州tialhビight a【川仙Pa行ぃnlMay2ユt（りune嵐9，1993，basedonJMÅ（japanMeteoro・log主ca王A酢nCy）．

急ぎ

Bulletin ofGlacierResearch

Potentialtemperaturegraduallyincreased（剛5K）

Bhalme，1976；Murakami，1976；Yasunari，1979eic．）．

below13km during the observationalperiod．The
potentialtemperatureshowedafluctuationofperiod

Similar long period fluctuation was noted in thetropospheric heat source over the eastern Tibetan

June15，quaSiwbiweeklyfluctuationwasobservedin
thisperiodwith，itsmaximumamplitudeinthelower
troposphere．

4L E）iurnaIvariationofthePBLinthepre−mOnSOOn

about5daysbeforeJune15withlar geamplitudein plateau（Nitta，1983），thoughlonger−periodosci11ation
thelayerbetween8and15km．Althotlghtheampli− （≠・g．intraseasoI−alvariation）ofabout30to40days
t11de oftbisperiod range was generaiiy smallafter
WaSStreSSediIl汰isstudy．

Figureld shows a time−height cross¶SeCtion of

tileSpeCificbumidity．HumidityirlCreaSedgradually（by−3g kg〝りar主d the deptb of the壬1umidiayer

increased during the observationalperiod．Specifichumidity of about6．5g kg¶1was observedin thelowestlOOOmdepthattheend ofJuly．AssociatedWith the northerly wind and fair weather，rapidSeaSOn

Tbed壬urnalvariationoftheverticalstructureof洩ePBLwasalsopromirlentdtlringfairveatberintbe
pre￣mOn＄00n SeaSOn．

Figure 3a shows the diurnal variation of thepotentialtemperatureprofilefromthesurface（5700ma．s．1）to8500m on May24，1993．Astablelayerwas
decreaseofhumidiとyoccurredperiodicallyonJunelO，Obser＼でdnearthesurfaceこItSunrise（08OOBST）．The
June22，Juiy6、andJuiy22．Theabruptmoistel血gStlrfaceskintemperaturestronglywarmedupasthe
OCCurredatJune15，June24，July9andJuly24when SunrOSeandthetemperaturedifferencebetweenthe
asoutherlywindblew．Theperiodofthefluctuationof
Surfaceandairbecameverylarge．Thislargediffer−thespecifichumiditybeforeJunelOwasshorterthan

払ata食erJunelO（arourld15days）．
Ås described above，tbe fluctuation w主tb period

about5dayswasprominentin each meteorologicalelement beforeJunelO．This fluctuation has thefo1lowingcharacteristics：1）southerlywindwascou▲

pledwithstrongwesterlywind，temperatureWaShighinthe写Vholeとroposphere，SpeC主f主chumiditywashigb
neartbestldace，2）wberlnOrtberlywindcoupiedwit‡1

Weak westerly wind blew，low temperature andhumiditywereobserved．
Thisphaserelationshipseemstoberelatedtothe
passageofthe troughembeddedin themid−1atitudeWeSteriiesovertbeTanggulamountains．Tbef王ucもu−atiorlWitbaperiodofabout5daysseems，therefore，
tocorrespondtothewesterlydisturbanceinmid…latト

ence suRgested that a large sensible heat flux wasprovidedた・Om払esurねce．Amixedlayerwitbnear−
1yu王Iiformpotendaltemperatureintbeverticaldeveト

Oped，anditstoplevelreachedabout2000mabovethe
Surfaceintheafternoon．Thepotentialtemperature
differencebetweenO800BSTand2000BSTwasabout

lOKin thelowestlOOOm．After sunset，the stablelayerwas formedneartbestlrねce and temperature

droppedinthePBL．
Figure3bshowsthediurnalvariationofthespe−

Cifichumidityprofile．Inthemorning（0800BST），thehumid layer was observed only below the surface
inversionlevel．Withincreaseinthe mixedlayer

deptれtbe‡nOisturewasalsomixedverticaliyinday−
time a‡1dbecamedryer．T壬Ie differeれCe Ofthe spe−cific humidity between 0800BST and 2000BST wasaboutl．7g kg．1in thelowestlOOO m．During theAfterJune10，Simi1artobeforeJunelO，SpeCific nightmoisture wasconfinedto thenocturnalbound−hlユmidityincreased（decrf≡aSed）withincreasein thearylayer，thelowerlayerbecamewetwithincreaseof
SOlitberly（れOrtherly）componerltOfwindintbeiowest
wind．
2000mof琉etroposphere．Lower欄freqtlenCy恥ct11a−
Figure 3c shows the diurnal variation of windtion with a period of15days was prominentin theSpeednearthe surface．Wind wasweakinthe sur−tudes．

meridionalwind during this period．The changein
the periodic fluctuation suggeststhat the summer
monsoonarrivedinthemiddleofJuneinTanggula，
Ⅵ㌢bicbisconsistentl好itbthedefinit主onoft壬IeOnSetOf

monsoon precipitationin this region（Ueno eial．，1994）．

Similarperiodicityhasbeenpointedoutoverthe
Asian summer monsoon region（Krishnamurtiand

faceinversionlayerand＄trOngabovethelayerinthe

mornlng．After the miⅩedlayer developed，wind
SpeedbecamealmostuniformverticallyinthemiⅩed
layer，Wbicbindicatestbatverticaimixingofmomen−
ttlmOCCurredinthemixedlayer．Duringthenight，

windwasveryweaknearthesurfaceandtheverticalgradientofwindspeedwaslargeabovethenocturnal
boundarylayer．

29

Endo（〜gαJ．

In払epre】−mOnSOOnSeaSOrl，aⅥ7eiトmixedverti（：alStruCtureOfuniねrmpoterltialtemperatlユreandmois−

turewasobservedonfairweatherdays，thoughYanai

and Li（1994）reported that moistureⅥraS‡10tmixed
Verticaliyirl偽e evenlng．Furtber studies on tile
VerticalstructureofhumidityⅥrOuldt〉eneeded．
In general，the depth of themiⅩedlayer may＄，58りCOrreSpOndto theintensity ofthe sensibleheat flux
6ナ0￠￠

fromtbesurface，Seasona‡aswe11asdilユrnaivaria＿

5，5榊Surfaceheatfluxesshouldbeexaminedasanextstep．

もionsoft‡1emixedlayerdep仏andassociatedregional

5，800
3144

5．Concludingremarks3ヱ6 3t8 320 322 324 326 328 330

Aero王ogicalobservationsⅥ7eremadefromthepre
MmOnSOOnSeaSOntOthemonsoonseasonintheTang仙

凱008

7，500

gula mountainsin the centralpart of the Tibetan

7彙800

lows：Plateau，Preliminaryresultsaresummarizedasfoト1）Warmingandmoisteningofthetropospherewere

ObservedfromMaytoAugust†Thetropopause

6，580

abruptlyroseatthebeginningoりune，Whicbmay
beassociatedwiththemigrationa‡1dthedeveiop−

6．000

mentoftbeSout‡トÅsia‡1anticyc！one．

5ナ5＄￠

5t￠￠0￠

0，52）Increaseofmoisturewasobservedinthesouther〜
1ywind．Ⅵrbennor払erlywindwaspredominant，也eatmospbereⅥデaSdryandcold．
3）Sbort period f】uctuatioms卜5days）were promi−

呈．5

1

‡，〕〔）

nent；They seeme to be associated witb the

passageofwesterlydisturbancesinthepre−mOn−
SOOnSeaSOrl．Tbesesflu（：tuationssuddenlycbaTl−gedintb．emiddleoりunetolongerper主od（〜15days）fluctuations，Whichcorrespondtotheonsetて、500

ofthemonsoonseason．

6，5004）well−developedmiⅩedlayerwasobscrvedonpre−mOnSOOnfairweatherdays；itstoplcvelreached6，0￠0abouと7000−8000m．Themoisturewasalsoweli

mixedvertically，andtbelayerbecamedry．

5，500
5，000
05‡￠

ま52025

F言g．3−（a）Verticaiprofi王eofpotentialtemperature（Kき，㈲SpeCifichumidity（gkgサ1），and（c）windspeed（msl）on
May24一Acknowledgments
This stも王dy was suppo豆ed by tbe Ministry ofEducation，Science and CuまtureInternationalScien・tific Research Program（No．01041043）．This

research was partly supported by the Special

ResearchProjectonGiobalEnvironmerltaiCha‡lgeat
theUni＼▼erSit〉lOfTsukuba．

30

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