Antarctic Meteorology

167 Pages·2001·3.46 MB·English

Antarctic Meteorology
Astudy with Automatic WeatherStations
Carleen Reijmer
Cover: Aerialphotograph of the Heimefrontfjellaand Automatic Weather Stations
5(photo’sbytheauthor)and4(photobyDanZwartz). Back: drawingcourtesyof
Pinguinxl,http://www.pinguinxl.nl/
Antarctic Meteorology
Astudy with Automatic WeatherStations
Antarctische Meteorologie
Eenstudiemetautomatischeweerstations
(meteensamenvattinginhetNederlands)
Proefschrift
ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van
deRectorMagnificus,Prof. Dr. W.H.Gispen,ingevolgehetbesluitvanhetCollege
voor Promoties in het openbaar te verdedigenop maandag24 september2001des
middagste12.45uur.
door
Catharina Helena Reijmer
geborenop21Januari1974,tePannerden.
Promotor: Prof. Dr. J.Oerlemans
faculteitNatuur-enSterrenkunde,UniversiteitUtrecht
This thesis is a contribution to the ”EuropeanProject for Ice Coring in Antarctica”
(EPICA), a joint ESF (European Science Foundation) / EC scientific programme,
fundedbytheEuropeanCommissionundertheEnvironmentandClimateProgram-
me (1994-1998)contract ENV4-CT95-0074and by national contributions from Bel-
gium,Denmark,France,Germany,Italy,theNetherlands,Norway,Sweden,Switzer-
landandtheUnitedKingdom.AdditionalsupportwasprovidedbytheNetherlands
AntarcticResearchProgramme(NARP)whichiscoordinatedbyNetherlandsEarth
andLifeSciencesFoundation(ALW)oftheNetherlandsOrganizationforScientific
Research(NWO).
ISBN:90-393-2802-1
Contents
Summary iii
1 Introduction 1
1.1 Background:climatechanges . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 TheEuropeanProjectforIceCoringinAntarctica . . . . . . . . . . . . 4
1.3 TheAutomaticWeatherStations . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Trajectorystudies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.5 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2 SurfacealbedomeasurementsoversnowandblueiceinTMbands2and4
inDronningMaudLand,Antarctica 15
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 Experimentalsetupandmeteorologicalconditions . . . . . . . . . . . . 18
2.3 Narrowandbroadbandalbedoofblueiceandsnow . . . . . . . . . . . 19
2.4 Bidirectionalreflectanceofblueiceandsnow . . . . . . . . . . . . . . . 27
2.5 Concludingremarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3 The annual cycle of meteorological variables and surface energy balance
onBerknerIsland,Antarctica 35
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Locationandexperimentalset-up . . . . . . . . . . . . . . . . . . . . . . 36
3.3 Meteorologicalconditions . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.4 Thesurfaceenergybalance . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.5 Summaryandconcludingremarks . . . . . . . . . . . . . . . . . . . . . 52
4 MeteorologicalconditionsinDronningMaudLand,EastAntarctica 55
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.2 Locationandexperimentalset-up . . . . . . . . . . . . . . . . . . . . . . 56
4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.4 Summaryandconcludingremarks . . . . . . . . . . . . . . . . . . . . . 75
ii CONTENTS
5 ThetemporalandspatialvariabilityofthesurfaceenergybalanceinDron-
ningMaudLand,EastAntarctica 77
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.2 Locationandexperimentalset-up . . . . . . . . . . . . . . . . . . . . . . 79
5.3 Prevailingmeteorologicalconditions . . . . . . . . . . . . . . . . . . . . 80
5.4 Modeldescriptionandvalidation . . . . . . . . . . . . . . . . . . . . . . 83
5.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.7 Concludingremarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6 MoisturesourcesofprecipitationinWesternDronningMaudLand,Antarc-
tica 99
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.2 TheAutomaticWeatherStations . . . . . . . . . . . . . . . . . . . . . . 101
6.3 Thetrajectorymodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.4 Modelandmeasurementcomparison . . . . . . . . . . . . . . . . . . . 103
6.5 Trajectoriesin1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
6.6 Casestudy: amajorsnowfalleventinMay1998 . . . . . . . . . . . . . 111
6.7 Summaryandconclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 115
7 Air parcel trajectories to five deep drilling locations on Antarctica, based
ontheERA-15dataset 119
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7.2 Thetrajectorymodel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
7.3 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
7.4 Resultsoftrajectorycalculations . . . . . . . . . . . . . . . . . . . . . . 127
7.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Bibliography 139
Samenvatting 149
Dankwoord 155
Listofpublications 157
CurriculumVitae 159
Summary
Thisthesischieflyaddressesa)theuseofAutomaticWeatherStations(AWS)inde-
termining the near-surfaceclimate and heat budget of Antarctica and, specifically,
DronningMaudLand(DML),andb)thedeterminationofsourceregionsofAntarc-
ticmoisturewiththeaidofatrajectorymodelandanatmosphericmodel. Thepri-
marymotivationbehindthisinterestisthedrillingoftwoicecoresintheAntarctic
ice sheet within the framework of the European Project for Ice Coring in Antarc-
tica(EPICA).Athoroughknowledgeofthemeteorologicalconditions willincrease
ourunderstandingoftheprocessesthatinfluencethesurfacemassbalanceandheat
budget.
In Chapter 2, ground-basedobservations of broadband, narrowband, and bidi-
rectionalreflectanceareusedtostudythealbedoofblueiceandsnow. Duringsum-
mer, surface albedo plays an important role in the amount of heat exchanged be-
tweenthesurfaceandtheatmosphere.Themainobjectiveofthestudyistoimprove
the methods used to derivesurfacealbedo from satellite measurements andarrive
atabetterunderstandingoftheprocessesinfluencingthemagnitudeofthealbedo.
Chapters3,4and5describethe dataobtainedfromten AWSinAntarcticaand
how they wereused to determine the local surfaceenergy budget. The AWSwere
placedontwotransectsperpendiculartothecoastlineinDMLandoneonBerkner
Island. As expected, mainly the strength of the katabatically forced flow, in com-
binationwith the geostrophic flow, determinesthe near-surfaceconditions atthese
locations. Thekatabaticflowvariesinstrengthdependingonthemagnitudeofsur-
faceslopeandtemperatureinversion, andisnotactiveonBerknerIsland,astation
onatopographicdome. InDML,thestrengthofthekatabaticflowvaries,resulting
inmaximumwind speedsandpotentialtemperaturesatthesiteswith thesteepest
slopes, at the edge of the Antarctic plateau. The annual mean wind speed varies
between 4 ms , near the coast and on the plateau, to 7 ms , on the edge of the
(cid:1)(cid:1) (cid:1)(cid:1)
plateau. The annual mean potential temperature varies between -18 C and -1 C.
Æ Æ
The annual mean temperature ranges from -16 C in the coastal area, where occa-
Æ
sional melt occurs, to -46 C on the Antarctic plateau. Owing to the low temper-
Æ
atures, the specific humidity is very low. Accumulation is highest in the coastal
regions and decreases with increasing elevation and distance from the coast, from
400mmwaterequivalentperyear(w.e. yr )nearthecoastto 30mmw.e.yr
(cid:1)(cid:1) (cid:1)(cid:1)
(cid:1)ontheplateau. (cid:1)
iv Summary
TheAWSdata,togetherwithamodelbasedonMonin-Obukhov similaritythe-
ory, areusedto calculatethe surfaceenergybudgetforthe measuring period. The
strengthofthekatabaticflowlargelydeterminesnotonlythenear-surfacemeteoro-
logical conditions but also the surface energy budget. The annual average energy
gainatthesurfacefromthedownwardsensibleheatfluxvariesbetween 3Wm
(cid:1)(cid:2)
to25Wm ,withthehighestvaluesatthesiteswiththehighest winds(cid:1)peedsand
(cid:1)(cid:2)
potentialtemperatures. Thenegativenetradiativefluxlargelybalancesthesensible
heat flux and ranges from 2Wm to 28Wm . The averagelatent heat flux is
(cid:1)(cid:2) (cid:1)(cid:2)
generally small and negati(cid:1)ve ( -1 Wm ), indicating mass loss through sublima-
(cid:1)(cid:2)
tion. Theannualsubsurfaceflu(cid:1)xesaresmall( -0.2Wm ).
(cid:1)(cid:2)
InChapters6and7,moisturesourcesofs(cid:1)now fallingatfivedeep-drillingloca-
tionsinAntarctica(Byrd,DML05,DomeC,DomeFandVostok)aredefined,based
on five-day backward air parcel trajectories calculated from data of the European
CentreforMediumRange WeatherForecasts. Basedon model precipitation, adis-
tinctionismadebetweencaseswithandwithoutsnowfallatthepointofarrival.Of
thesnowfalltrajectoriesendingatDML05in1998,40-80%originateintheAtlantic
Ocean between 40 and 60 S, within four days before arrival. Evaporation along
Æ
these trajectories is largest during the first half. A case study for May 1998shows
thatduringsnowfallexceptionallyhightemperaturesandwindspeedsprevailinthe
atmosphericboundarylayer. ThetrajectoriesfromtheECMWFRe-analysisProject
(ERA-15)covera15-yearperiodandshowthattheoceansclosesttothefivedrilling
sitescontributemost ofthemoisture. Thelatitudebandcontributingmost ( 30%)
ofthetotalannualprecipitationisat50-60 S,theareajustnorthoftheseaice(cid:1)edge.
Æ
Thecalculatedtrajectoriesshow seasonaldependency,resultingin aseasonalcycle
inthemoisturesources,whichisfurtherenhancedbyaseasonalcycleintheamount
ofprecipitation.
Chapter 1
Introduction
1.1 Background: climate changes
In the history of the Earth, the climate has changed considerably numerous times
(Dansgaardetal.,1993;GreenlandIce-coreProject(GRIP)Members,1993;Petitetal.,
1999). The variability in the Earth’s climate system is causedby naturalvariations
infactorssuchassolarinsolation,oceancurrentsandatmosphericcompositiondue
to,forexample,volcaniceruptions. Duringthelastcentury,climatehasbeenaddi-
tionallyinfluencedbyanthropogenicsources,e.g.,CO andmethaneemissionsfrom
fossilfuelburning.Thesensitivityoftheclimatesystem(cid:2) tochangesin,e.g.,insolation
oratmosphericconstituents,differsperregion.Climatestudieshaveshownthatthe
polarregionsaremoresensitivetoclimaticchangesthanotherregionsowingtothe
albedo feedback mechanism (Oerlemans and Bintanja, 1995). Viewed in this light,
theAntarcticandGreenlandicesheetsareinterestingregionstostudy,alsobecause
of their potential contribution to sea level rise. The Greenlandice sheet represents
a potential sea level rise of 7 m and complete melting of the Antarctic ice sheet
wouldraisethesealevelby (cid:1)60m.Incomparison,thefreshwaterstoredinglaciers
andsmallicecapsrepresent(cid:1)sapotentialsealevelriseof 0.5m(IPCC,1995).
Notonlythe(changing)conditionsonthesurfaceofth(cid:1)eGreenlandandAntarctic
icesheetsyieldvaluableinformation,theiceitselfalsocontainsawealthofhistoric
climate information. Data pertaining to past climate and state of the local atmo-
sphere,suchastemperature,chemicalcompositionandatmosphericcirculation,are
storedintheice.Owingtotheconsiderablethicknessoftheice(3000to4000m)and
the low accumulation rate, the length of the recordsthat can be obtained is on the
orderof150to500kyr.Theserecordsincludeseveralglacial-interglacialcycles(Petit
etal.,1999).Togainaccesstotheseclimaterecords,severaldeepicecoreshavebeen
drilledintheAntarcticandGreenlandicesheet, e.g.,Vostok, Byrd,DomeF,Taylor
dome (Antarctica),GreenlandIce CoreProject (GRIP and North GRIP) andGreen-
land Ice Sheet Project (GISPII) (see for example Greenland Ice-core Project (GRIP)
Members(1993);Dome-F Ice CoreResearch Group (1998b);Petit et al. (1999);Mul-
vaney et al. (2000)). These ice cores have provided insight in the climate at these
2 Chapter1.Introduction
-410
a
‰) -420
s ( -430
s
ce -440
x
m e -450
u -460
uteri -470
De -480
-490
300
b
280
v)
m 260
p
p
(2 240
O
C 220
200
180
0 50 100 150 200 250 300 350 400
Age (kyr BP)
Figure1.1. Timeseriesof(a)deuteriumexcessand(b)CO intheVostokicecore,Antarctica
(Petitetal.,1999).CO ispresentedinpartspermillionvolu(cid:1)me(ppmv).
(cid:1)
locations over the past 150 to 400 kyr, through the isotope composition of the ice
itself, the presenceof other elements in the ice, and the composition of airbubbles
enclosed in the ice. Figure 1.1 presents an example of records obtained from the
Vostokicecore,Antarctica.Deuteriumexcessisoftenusedasaproxyforairtemper-
atureandrepresentsalocalsignal. CO isstoredintheairbubblesandmarksglobal
variationsinatmosphericcomposition(cid:2).
Theinterpretationoftheobtainedrecordsis,however,notstraightforward. The
climatic record is of little value unless the age of the ice is known as a function of
depth. Counting annuallayersis themost exactmethodof determiningthe ageof
theice. Whentheannuallayersaretoothinandthedatesofvolcanicashhorizons
not well known or no volcanic horizons are present, dating the ice relies on com-
parison with other dated climate recordsand ice flow modelling (Patterson, 1994).
Thisintroducesadditionaluncertaintiesandcanresultincompletelydifferentinter-
pretations of ice core records(Mulvaney et al., 2000). A further problem is how to
relatetheobtainedrecordsof, e.g.,isotope content (e.g.,hydrogenandoxygen iso-
topes)andgascomposition(suchasCO andCH )tothestateoftheatmosphereat
agivenpointintime. Theclimaterecord(cid:2)edinice(cid:3)coresismainlydeterminedbythe
localsnowfallconditionsandbytheoriginoftheairandmoisture.Theconditionsin
whichsnowfalloccursneednotrepresentthemeanconditionsatthatpoint(Noone
andSimmonds,1998;Nooneetal.,1999).Severalfactors,suchaschangesinseason-
alityofsnowfallandchangesinmoisturesourceregions(Jouzeletal.,1997;Werner
etal.,2000),maybiastheicecorerecord.
Thestable-isotoperatiosofhydrogen( D)andoxygen( O)intheiceareexam-
(cid:1)(cid:4)
plesofhow icerecordsarerelatedto climÆatesignalsandaÆreoftenusedasaproxy
for temperature (Petit et al., 1999). In Antarcticice core records, temperatureis of-