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ATMOSPHERICTRANSPORTPROCESSESOVERTHEKATHMANDUVALLEYNEPAL ATMOSPHERICTRANSPORTPROCESSESOVERTHEKATHMANDUVALLEYNEPAL ATMOSPHERICTRANSPORTPROCESSESOVERTHEKATHMANDUVALLEY,NEPAL ATMOSPHERICTRANSPORT PROCESSES OVER THE KATHMANDU VALLEY, NEPAL RPRidLkNJh RamP.RegmiandLokN.Jha Ram P. Regmiand LokN. JhaCentralDepartmentofPhysicsTribhuvanUniversityKathmanduNepalSCIENCE AND TECHNOLOGY 2011 T1P13 TRIBHUVANUNIVERSITYCentral Department of Physics, TribhuvanUniversity, Kathmandu, Nepal.SCIENCE AND TECHNOLOGY 2011: T1-P13 TRIBHUVAN UNIVERSITY
ABSTRACT5ResultsCVerticalStructureofWindandPotentialTemperatureTemporalandSpatialDistributionofPollutants ABSTRACTThitthtitithKthdllhbtdidtthtildtl
5.ResultsAChtitifNSfLlFl
C. Vertical Structure of Wind and Potential TemperatureTemporal and Spatial Distribution of Pollutants() TheairmasstransportcharacteristicsovertheKathmanduvalleyhavebeenstudiedtoassessthespatialandtemporal
dbfdlfllhhlflThdhbdhhlfA.Characteristics of Near Surface Local Flows
06:45LST 00:45LST18:00 LST •Pollutants(e.g.,SO2)releasedinthesouthernareabuildshihihd distributionsofdecouplingofvalley'sairmasswiththeregionalflows.Thestudyhasbeencarriedoutwiththeapplicationsof
06:45 LST 00:45 LST Near surface wind at 11:45 LST Near surface wind at 05:45 LSThighconcentrationzoneneartheeasternandthttil fpgfygfyppf
MesoscaleMeteorologicalModel(MM5)WeatherResearchandForecast(WRF)andaChemicalTransportnortheasternmountainslops.
MesoscaleMeteorologicalModel(MM5),WeatherResearchandForecast(WRF)andaChemicalTransportMdlThdlditihbdithbddtThtdlthtKthdlltill
•TheprevailinglocalflowsorganizegeneralmassModels.Themodelpredictionshavebeencomparedwithobserveddata.ThestudyrevealsthatKathmanduvalleytypicallyPa)
Pa)
pgggtransportfromwest/southtoeastintheKathmandu
showsaplateau-basindualnature.Thenighttimenearsurfaceairmassremainslargelycalm.However,theintermittentre (h
e (hP
valleyandchanneloutintoeasternvalley.Thepollutants pTgfgyH,downslopewindsorganizeaweakflowsystemthatoftendevelopsvalleywideanticlockwisecirculationatabout150mabovethessur
ssure
L m)furthermovetowardstheHimalayas.
downslopewindsorganizeaweakflowsystemthatoftendevelopsvalleywideanti-clockwisecirculationatabout150mabovetheflhhllbffldhhllflddhhT
Pres
Pres
SL
m)
MSL
e (km
•SOremainsconstantaround40ppbduringthe floor,whichslowlybuteffectivelyinducesmassexchangeinthelowerlayerofcoldairmassduringthenighttime.TwoveryAM
e (km
m) A
M
ance•SO2remainsconstantaround40ppbduringthenighttimedespiteitscontinuousreleaseinthearea
gentlewindsystems,southwesterlyandnorthwesterly,composedofregionalscaledeepupslopeandplain-to-plateauwinds(m)
ance
n (m
istanighttimedespiteitscontinuousreleaseinthearea(Imadol)duetothewindlesssurfaceandpresenceof gentlewindsystems,southwesterlyandnorthwesterly,composedofregionalscaledeepupslopeandplaintoplateauwinds
llitditthKthdlllttidtitillthltiUifth3ion
Dista
ation
th D(Imadol)duetothewindlesssurfaceandpresenceofsomeintermittentwindatabout150mAGLas regularlyintrudeintotheKathmanduvalleyclosetonoontimeandcontinuetillthelateevening.Upperairfrommorethan3
kbhllddhllflhfSfKhd
evati
th D
leva
Nortsomeintermittentwindatabout150mAGLas
mountain/down‐slopewind.kmabovethemeansealevelcomesdownandsweepsacrossthevalleyfloorintheafternoon.SpringseasonofKathmanduEle
Nort
n El
uth-Nmountain/downslopewind.
ThditibtifllttdttthdilappearstoberelativelywindycomparedtowinterNostrongdecouplingofvalley'sairmasswiththeregionalairflowsappear12:45LST 10:45LST rain
uth-N
errai
Sou•Thedistributionofpollutantsdemonstratethediurnalidiitiittiththhtiti appearstoberelativelywindycomparedtowinter.Nostrongdecouplingofvalleysairmasswiththeregionalairflowsappear
titfth2hiddthllThditittillthtd12:45 LST 10:45 LST
Terr
Sou
Te Speriodicityinconsistentwiththecharacteristicmeteorology topersistformorethan24hoursorsoinandaroundthevalley.Thesurroundingmountaintops,particularly,theeasternand
hbhblflbkdl
Tmeteorology.
southeasternmountaintopsappeartobethemostsuitablesitesforregionalbackgroundaerosolconcentrationmeasurements.•Pollutantsmayspreadoverthemixedlayerofabout1.2 pppfgg
1Idi
Pa)
Pa)kmoverthevalleyjustbeforetheintrusionofthelocal1. Introductione (hP
e (hP
flows.
Mt. ShivapuriMt. Nagarkot TheatmospherictransportprocessesovertheKathmandussure
ssure
•IntheeveningHNO3richairmasscomesbackovertheMt. Phulchoki
2660 m2250 m TheatmospherictransportprocessesovertheKathmanduvalleylocatedintheMiddleHillsoftheCentralHimalayaP
res
Pres
West-EastDistance(km) West-East Distance (km)IntheeveningHNO3richairmasscomesbackovertheKathmanduvalleyandremainsfloatingatabout350 2762 m valley,locatedintheMiddleHillsoftheCentralHimalaya,
offersratherdifferentcharacteristicsoflocalflowfieldsin
P P West-East Distance (km)
Nearsurfacewindat14:45LSTNearsurfacewindat17:45LSTKathmanduvalleyandremainsfloatingatabout350metersabovethevalleyfloor. offersratherdifferentcharacteristicsoflocalflowfieldsin
comparisontothegeneralmountainvalleywindsystemInNear surface wind at 14:45 LSTNear surface wind at 17:45 LSTmetersabovethevalleyfloor.
comparisontothegeneralmountainvalleywindsystem.Inthisregionthelocalcirculationsassociatedwithalarge thisregion,thelocalcirculationsassociatedwithalargenumberofsmallscalesubdivisionsandsubclimatesinteract numberofsmall‐scalesubdivisionsandsub‐climatesinteractinacomplicatedmannerPresentstudyassessesthe inacomplicatedmanner.PresentstudyassessestheatmosphericconditionsprevailingovertheKathmanduvalley17:45LST atmosphericconditionsprevailingovertheKathmanduvalleyandthenexaminestheextentofdecouplingofsurfaceair
17:45 LST 14:45 LST
L m)
m)
andthenexaminestheextentofdecouplingofsurfaceairiddthKthdlliththilM
SL
(km
MSL
(km
D3 TheonlyValleyOutletmassinandaroundtheKathmanduvalleywiththeregionalfldithdddititbl
AM
nce
) AM
nce
D3 The only Valley OutletBagmatiRiver Gorge flowsduringthedryseasonandrecommendssitessuitable
fil/lbllbkdttiPa)
Pa)
(m)
stan
n (m)
stan
forregional/globalaerosolbackgroundconcentrationtWeakStability e (hP
(hP
on (
h Dis
tion
Dis
measurement.StableLayer(1km)
Weak Stability
ssure
sure
vatio
orth
evat
rth
Stable Layer(~1km)
Pres
Press
Elev
th-N
n Ele
Nor
P P
in E
Sout
rrain
uth-
View in AutumnHimalayasrrai S
Ter
Sou
Tihiht()AMSL
yC TeS
Terrain height (m) AMSL3DTopographicViewofKathmanduValleyandItsSurroundingsShllthtl
CB
3‐D Topographic View of Kathmandu Valley and Its Surroundings.()
Shallow southwesterly
hhllfl()dd(l) BhimsenTower (54m high)Northwest‐Southeast cross‐sectional plot of potential temperature (contours) and wind vector (along A—B)
S 17:45 LST West-East Distance (km)West-East Distance (km)
KathmanduremainrelativelycleanduringAutumn
()()Near surface wind at 20:45 LST
Kathmandu remain relatively clean during AutumnConceptual flow diagram
Vtildiifllttiltiita)
Vertical dispersion of pollutants in late morning winter
(hPa
Himalayan range as seen from Kathmanduure (
Hundreds of emitters in operation
ressuPr
SL
m)
AM
e (km
(m)
ance
SodarsiteNthtlflbthtl ion
ista
Northwesterly flows above southwesterly
evati
th D
Southwest‐Northeast cross‐sectional plot of potential temperature ()()
Photographs of wind/dust storm (upper left picture) and highly Ele
Nort
Smokeflowpatternintheafternoon Fogandpollutant’slayerblanketingtheKathmanduValley(contours) and wind vector (along C—D)localized destructions caused by wind storm in last March.
rain
uth-N
Smoke flow pattern in the afternoon Fog and pollutants layer blanketing the Kathmandu Valley
2GllitiftfKthdll•Bothsouthwesterlyandnorthwesterlyshowthenatureofthecooldensity•Therelativelycoolersouth‐westerlycappedbythewarmer Terr
Sou
2. General climatic feature of Kathmandu valleyyyy
flow;theyintrudeintothemixedlayerdevelopedovertheKathmanduyyppy
northwesterlyandthedevelopmentofstablelayeraloftjustT S
TheKathmanduvalleypossessesawarmtemperatesemi‐tropicalandvalley.abovethesurroundingmountaintopsthatcoversthewhole TheKathmanduvalleypossessesawarmtemperatesemitropicalandseasonableclimate.Thewinterclimateischaracterizedasdrywithan•Thesouthwesterlyisdrivenbyacombinationofbothupslopeandplain
Kathmanduvalleyandbeyondsetsthebasicmeteorological yaveragemaximumandminimumtemperaturesof17and2°C,
•Thesouthwesterlyisdrivenbyacombinationofbothup‐slopeandplain‐to‐plateauwinds
backgroundforairpollutiontransportoverthevalley. gp,respectively.Duringthewinterseason,thevalleyremainsmostlyclear
to‐plateauwinds.•Thislayeringflowstructureoverthevalleyseverelylimitsthe pyg,yy
initsskieswithcalmorwindlessnightsfollowedbyearlymorning•ThenorthwesterlyexecuteahydraulicjumplikeflowanditridesovertheThislayeringflowstructureoverthevalleyseverelylimitstheverticaldispersionofpollutantsandleadstotheformationof WestEastDistance(km)
densefoglingeringupto09or10LocalStandardTime(LST).Verycoolsouthwesterlythedepthofwhichisabout250m.verticaldispersionofpollutantsandleadstotheformationofmultiplelayeringofpollutants.
West-East Distance (km)
gentlewindroutinelystartstoblowclosetothenoontimeand•Thewindstormgenerallyoccurslateafternoonandearlyeveningthatmultiplelayeringofpollutants.
Thidllldl700800bhNighttime Wind Fields at 02:45 LST at 150m AGL Near surface Potential Temperature at 16:45 LST
7ObservedLocalFlowCharacteristicsinandAroundtheValley LocalFlowsandObservedPollutantDistribution continuetilltheevening.ThesurfacewindspeedshavebeenfoundtoThewindstormgenerallyoccurslateafternoonandearlyeveningthatcoincideswiththedevelopmentofstablelayerjustabovethesurrounding•Themixedlayergenerallydevelopsupto700to800mabovethe
llflithftdithd
7. Observed Local Flow Characteristics in and Around the Valley Local Flows and Observed Pollutant Distribution
becalm(<1ms‐1)forabout75%ofthetimeofadaywithmax.windpyjg
mountaintops.valleyfloorintheafternoonduringthedryseason.Wind Speed at Thankot (March)
10.01-Mar2M
Wind Speed at NAST (March)6.01-Mar
Wind speed at western mountain passWind speed at southern area
speedgenerallyaround5ms‐1intheafternoon,butcouldreachashighp
DEmissionSourceDistributioninDrySeason9.0
2-Mar3-Mar4-Mar
2-Mar3-Mar4-Mar
as15ms‐1inthelatespring.SpringmonthsarecharacterizedbyD. Emission Source Distribution in Dry Season8.0
a5-Mar6-Mar7-Mar
5.04Mar5-Mar6-Mar7Mar
showeryandrelativelywindyweather,increasinglyhigherhumiditydhdihilhilWidNOTSP SO
7.0
7-Mar8-Mar9-Mar10Mar40
7-Mar8-Mar9-Mar10M
andpre‐monsoonthunderstormswithoccasionalhail.Winterandlihditthtidth
NOxTSP SOx )6.0 m/s)10-Mar
11-Mar12-Mar
4.0
m/s)10-Mar
11-Mar12-Mar
earlyspringshowersmaydepositsnowonthemountainsaroundthedfthllThidttldftill(km
m)5.0 peed (13-Mar
14-Mar15-Mar3.0 peed (m
13-Mar14-Mar15-Mar
edgesofthevalley.Thewindpatterns,cloudformation,valleyventilationvisibilityaswellastheairmassdispersioncharacteristicsnce (
e (k
4.0
Wind sp15Mar
16-Mar17-Mar18-MarW
ind Sp15Mar16-Mar17-Mar18-Mar
ventilation,visibilityaswellastheairmassdispersioncharacteristicsoverthevalleyindryseasonappearsdistinctlydifferentfromthewetAil stan
ance
3.0
W18-Mar19-Mar20-Mar21M
2.0
W18-Mar19-Mar20-Mar21Mar overthevalleyindryseasonappearsdistinctlydifferentfromthewet
seasonThesummermonsoonoccursaseasterndisturbancesTheAprilApril
h Dis
Dista
2.021-Mar22-Mar23-Mar
10
21-Mar22-Mar23-Mar24M season.Thesummermonsoonoccursaseasterndisturbances.The
annualrainfallgenerallyexceeds1300mmofwhich70to80%rainfallsorth
rth D
1.024-Mar25-Mar26-Mar
1.024-Mar25-Mar26-Mar
annualrainfallgenerallyexceeds1300mmofwhich70to80%rainfallsduringthesummermonsoonmonthsMonsoonrainshaveatendencyh-N
-Nor
0.0
000000000000
26Mar27-Mar28-Mar29Mar0.0
27-Mar28-Mar29-Mar duringthesummermonsoonmonths.Monsoonrainshaveatendency
tobemorefrequentatnightwhereasthedaylighthoursaremostlySout
uth-0:00
2:00
4:00
6:00
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
LlStddTi(h)
29-Mar30-Mar31-MarA
0:00
2:00
4:00
6:00
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:0029Mar30-Mar31-MarAverage tobemorefrequentatnightwhereasthedaylighthoursaremostly
sunnyOvercastisratherrareoverthevalleyThedryseasongenerally
S
SouLocal Standard Time (hr.)AverageLocal Standard Time (hr.)Average
sunny.Overcastisratherrareoverthevalley.Thedryseasongenerallypersistsfor9months(OctobertoJune)withmuchlessprecipitation
Wind Speed at Babarmahal (March)4.51-Mar
2M
Wind Speed at Budanilakantha (March)5.01-Mar Wind speed at northern area Wind speed at central area persistsfor9months(OctobertoJune)withmuchlessprecipitation
(only10–20%oftheannualtotal).4.0
2-Mar3-Mar4-Mar4.5
a2-Mar3-Mar4-Mar (only1020%oftheannualtotal).
35
4.05-Mar6-Mar7-Mar4.0
4-Mar5-Mar6-Mar7Mar
3. Purpose30
3.57Mar8-Mar9-Mar10Mar
3.5
7-Mar8-Mar9-Mar10M
•TounderstandthemechanismofdevelopmentoflocalflowsovertheKathmanduvalley25
3.0
(m/s)10-Mar
11-Mar12-Mar13M
3.0 m/s)10-Mar
11-Mar12-Mar
•TounderstandthemechanismofdevelopmentoflocalflowsovertheKathmanduvalley.Tdtdhifilltittdthidithll
2.5
peed (13-Mar14-Mar15-Mar2.5 peed (13-Mar
14-Mar15-Mar
•Tounderstandmechanismofairpollutiontransportandtheirdynamicsoverthevalley.Tdtdthltihibtthllfldftifthllttfildithll
FebruaryFebruary WestEastDistance(km)
2.0
Wind S16-Mar
17-Mar18-Mar
2.0
Wind S15Mar
16-Mar17-Mar18Mar
•Tounderstandtherelationshipbetweenthelocalflowsandformationofthepollutantfieldsinthevalley.Thildldiibifdlifll’iihhilfl
West-East Distance (km)West-East Distance (km)1.5 W18-Mar19-Mar20-Mar21Mar
1.5
W18-Mar19-Mar20-Mar21M
•Toassessthespatialandtemporaldistributionsofdecouplingofvalley’sairmasswiththeregionalflows.ff21 21 MoreLargeScaleFlow
1.021-Mar22-Mar23-Mar24M
1.021-Mar22-Mar23-Mar
ObdNOdSOllfllthiltdll•Kathmanduvalleyremainscalmduringlateeveninguntil
•Toidentifythesuitablesitesforregionalbackgroundaerosolconcentrationmeasurement.NOx(kg-NO2 km-2day-1)TSP (kgkm-2day-1) SOx(kg-SO2km-2day-1) More Large Scale Flow0.524-Mar25-Mar26-Mar
0.524-Mar25-Mar26-Mar
•Observed NO2and SO2closely follows the simulated local fl
thenoonformingadeepcoldairlakeatnightthatmay
4Methodologyx2
EVisibleTransportProcesses 4.MethodologyNearSurfaceWindFieldsat14:45LST0.0
000000000000
26Mar27-Mar28-Mar29-Mar
0.0
000000000000
26Mar27-Mar28-Mar29Mar
flows. reach400minitsdepthintheearlymorning.4.MethodologyE. Visible Transport Processes 4. MethodologyNear Surface Wind Fields at 14:45 LST
0:00
2:00
4:00
6:00
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:0029-Mar30-Mar31-MarAverage
0:00
2:00
4:00
6:00
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
LlStddTi(h)
29-Mar30-Mar31-MarA •TheAprilconcentrationsaresignificantlyhigherthanthe •Intrusionofcoolerairmassesclosetothenoontimefrom
NagarkotHilltopLocal Standard Time (hr.)AverageLocal Standard Time (hr.)Average TheAprilconcentrationsaresignificantlyhigherthanthe
Februarybutthedistributionpatternremainsthesame. theIndianPlainandthewesternvalleythatmergeintoa
A.Air pollutionNagarkotHilltop
•UpwardtransportofsmokeatthefrontoflocalflowsrevealtheFebruarybutthedistributionpatternremainsthesame.Thismayindicatetheatmosphericconditionsdrivingthe•Diurnalvariationoftheobservedwindoverthevalleyfloorcanbecharacterizedwitha westerlyformingconvergencealongcentralwest‐east p
DtilfildtfNO2dSO2
Upwardtransportofsmokeatthefrontoflocalflowsrevealthepassageofthefrontclosetothenoontime.
Thismayindicatetheatmosphericconditionsdrivingthelocalflowsareratherstableduringthedryseasonandthus
longperiodofthecalmsituation,from20:00LSTto10:00LSTonthenextday,andonset line.•DetailfieldmeasurementofNO2andSO2,
dPM10kli
passageofthefrontclosetothenoontime.localflowsareratherstableduringthedryseasonandthuslocalflowstendtorepeatregularly
ofthewindataround12:00LST,whichcontinuestoaround18:00LST. •Thewarmernorthwesterlyflowsoverthecoolersouth‐andPM10atkeylocations
kkd•Thepollutantsreleasedintothesouthwesterlyaretrappedinits )
localflowstendtorepeatregularly.•Thecalmsituationcorrespondstothestablystratifiedcoldairlakeduringthenighttime, westerlyinthelateafternoon.•Emissionestimation1kmx1kmgridnet.shallowlayerbelow250mhighandmigratetowardtheeasternpartof T(m
)
•VeryhighconcentrationoftheNO2andSO2inAprilandtheunsetofwindrepresentsarrivalofacombinedvalleyandtheplain‐to‐plateaudfhhblldhhl
y•Combinedplain‐toplateauandvalleywindfromthe
•NumericalsimulationwithChemicalTransportModel.yggp
thevalleyT
on (
measurementcomparedtoFebruarysuggeststhewindsformtheneighboringvalleyandthesouthernplain.ThflhkblddiiliAbli
ppysouthernplain(southwesterly)andnorthwesterlyform
BMeteorologyNagarkotHilltop
thevalley.
KSatio
advectionofregionalpollutantsintothevalleywithlocal•Thepatternsofmeteorologyhavearemarkableday‐to‐daysimilarity.Anyabnormalitytitildldttlltiftti
p(y)ythewesternvalleystronglydominatetheflowsystemof B.MeteorologyNagarkotHilltop •Thenorthwesterlycapturestheurbanpollutantsinthewesternpartof Keva
flows.apparentinaparticulardayrarelyordoesnotatallcontinueevenfortwoconsecutived
thewesternvalleystronglydominatetheflowsystemofKathmanduvalley(K).
•SodarobservationusingMonostaticFlatArraySodar.yppp
thevalleyandflowsoverthesouthwesterlylayer. n Eldays.
6SitfRilBkdAl
Kathmanduvalley(K).•Flowsplitintheeasternvalley(S)appearsratherweak
•SurfaceobservationsinandaroundtheKathmanduvalley.thevalleyandflowsoverthesouthwesterlylayer.
ain6. Sites for Regional Background Aerosol 8Conclusions
Flowsplitintheeasternvalley(S)appearsratherweakanddoesnotpenetrateKathmandu y
•NumericalSimulationoflocalflowswithMM5andWRF.•Asaresult,multiplepollutantlayersdevelopintheeasternareaofthe
TerrConcentration Measurement8. Conclusions anddoesnotpenetrateKathmandu.
•LocalflowsappeartofollowtheterrainelevationKTMvalleyclosetothesunset.
Te
TribhuvanUniversityNagarkotHilltop•LocalflowsappeartofollowtheterrainelevationKTMvalley(K)1350mSunkoshi(S)800mTrishuli(T)600mvalleyclosetothesunset.TribhuvanUniversityNagarkotHilltop•Kathmanduvalleyregularlydevelopsadeepcalmcoldairpoolduringthenighttime. valley(K)1350m,Sunkoshi(S)800m,Trishuli(T)600mvalleys;southernplain(~100m)AMSL
FinestDomain(D3) 45050FChilTtCllti
HattibanHilltop•Twocharacteristicslocalflows(southwesterlyandnorthwesterly)regularlyintrudeintothe valleys;southernplain(~100m)AMSL.Itittttiididti Finest Domain (D3) 450TirshuliF. Chemical Transport Calculations
hflllfllfll
pvalleyclosetothenoontimeandcontinuetilltheevening. •Intermittentmountainwindsmayorganizedananti‐
lkikfltthllb150Daytime Characteristic of Pollutant Transport Role of Local Flows for Pollutant Transport•Thereislittleday‐to‐dayvariationinthelocalflowsoverthevalleyduringthedryseason.clockwiseweakflowsystemoverthevalleyabove150mkihibllidl
07:00LST12:00LST15:00 LST15:00 LSTyyygy
•Thelocalflowsshowthenatureofcooldensityflowsintrudingintotheweaklydevelopedkeepingtheairmassbelowalmostwindless.
hdlll/bdl07:00 LST12:00 LST
m)
m) 36040Mt. Shivapuri
WestEastDistance(km)
ygypmixedlayeroverthevalley. •Kathmanduvalleyexecutesplateau/basindualnature
(km
(kmTNWest‐East Distance (km)mixedlayeroverthevalley.•Therelativelywarmernorthwesterlyflowsoverthecoolerandshallowsouthwesterly
duringdayandnighttime.
ce
ce (
BUMtNagarjunFulchokiMountaintop
Therelativelywarmernorthwesterlyflowsoverthecoolerandshallowsouthwesterlyduringthelateafternoonleadingtotheformationofinternalthermalboundarylayersin BComparisonwithObservation
anc
tanc
Mt. EverestNEPAL 27030
TL MH BAMt. Nagarjunpduringthelateafternoonleadingtotheformationofinternalthermalboundarylayersin
thecentralandeasternarea
B. Comparison with Observation
Dist
Dist N E P A L 27030
TIA THBTMtNagarkot
Kathmanduthecentralandeasternarea.Thifth3kbthlllldd
th D
th D
KathmanduTIA
KLBS MA
BTDAMt. NagarkotBhaktapur D3
•Theupperairfrommorethan3kmabovethemeansealevelregularlycomesdownandthllflithft
Nort
Nort
BKTI KRPUBS MABhaktapur
Patan D3sweepsacrossthevalleyfloorintheafternoon.f
h‐N
th‐N
D2 18020BN BK
IM HCNK Mt. Champadevi•Thedownslopewindscanorganizeaweakflowsystematabout150mabovethevalley •FulchokiMountaintop(2762AMSL),locatedinthe
X2 outh
out D2 18020LU IM HC
Banepafloorthatslowlybuteffectivelyinducemassexchangeinthelowerlayerofcoldairmass southeasternedgeoftheKathmanduvalleyappearstobe
18:00LST 15:00LSTX2
SoSo
CH
Banepa•Duringthenighttimepollutantaccumulatesintheshallowlayer.duringthenighttime. mostsuitablefortheregionalaerosolmeasurement.
18:00 LST 15:00 LST CHRiverGorge
Duringthenighttimepollutantaccumulatesintheshallowlayer.
lldiidlhidllfi•Kathmanduvalleyregularlyflushesitsnighttimestagnatedairmasstotheeastern •ThesitessuchasNagarkotHilltopandHattibanHilltopand
ibhiilbbliblf 9010Mt.FulchokiRiver Gorge•Pollutantsdisperserapidlyasthemixedlayerevolvesaftersunrise
ttdiiittitthneighboringvalleyintheearlyafternoonthatfurthermovestowardstheHimalayas. TribhuvanUniversityalsoappeartobereasonablysuitablefor
itithilbkdttifi
Kthdll INDIAMt. Fulchokiattendingaminimumconcentrationatthenoon.
ggyyy•Thewesternpartofthevalleyappearstobefreefromdaytimestratification.
monitoringtheregionalbackgroundconcentrationofspecieslikdiit Kathmandu valley D1•Intrusionofthecoolersouthwesterlytrapsthepollutantreleasedwithin
pyppy•Occasionaldecouplingofvalley’ssurfaceairmassdoesnotsustainformorethan24hours.
likeradioxenonisotopes.
360
yppitsshallowboundaryrapidlybuildingupnearsurfaceconcentration.
Occasionaldecouplingofvalleyssurfaceairmassdoesnotsustainformorethan24hours.•Thepollutantsfromtheeasternvalleyintheeveningremainfloatingoverthewholevalley
WtEtDit(k)901802703604501020304050•Thefictitiouspollutants(X1andX2)concentrationdistributioncontours
Thepollutantsfromtheeasternvalleyintheeveningremainfloatingoverthewholevalleyatabout250mabovethevalleyflooruntilthedevelopmentofmixedlayernextday Akldt West‐East Distance (km) West‐East Distance (km)•Thefictitiouspollutants(X1andX2)concentrationdistributioncontours
clearlydemonstratethedoublelayeringstructureofthesouthwesterlyatabout250mabovethevalleyflooruntilthedevelopmentofmixedlayernextday. Acknowledgment:
•TohsihiroKitadaToyohashiUniversityofTechnologyJapanMM5/WRF/CTM Simulation Domain System D1, D2, and D3 (left) and Air Quality Sampling Sites (Black Circle).
clearlydemonstratethedoublelayeringstructureofthesouthwesterlyandnorthwesterlywindsandformationofthelayeredpollutantsover
•TohsihiroKitada, Toyohashi University of Technology, Japan•HarryMileyPacificNWNationalLaboratoryUSA
Blue and Red boxes show emission areas (right) for the hypothetical species X1 and X2, respectively.andnorthwesterlywindsandformationofthelayeredpollutantsoverthecentralandeasternareaoftheKathmanduvalley
•Harry Miley, Pacific NW National Laboratory, USA.•AndersRingbonSwedishDefenseResearchAgencySwedenContact:regmirp@hotmailcom (g)ypppythecentralandeasternareaoftheKathmanduvalley.•Anders Ringbon, Swedish Defense Research Agency, Sweden.Contact: [email protected]