Atmospheric circulation and the surface mass balance in a regional climate model of Antarctica [Elektronische Ressource] / von Ksenia Glushak

Ksenia Glushak

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• Publié par: universitat_potsdam
• Publié le: 01 janvier 2008
• Nombre de lectures: 19
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

Atmospheric circulation and the surface mass balance
in a regional climate model of Antarctica. Dieses Werk ist unter einem Creative Commons Lizenzvertrag lizenziert:
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Elektronisch veröffentlicht auf dem
Publikationsserver der Universität Potsdam:
http://opus.kobv.de/ubp/volltexte/2008/1729/
urn:nbn:de:kobv:517-opus-17296
[http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17296] Atmosphericcirculationand
thesurfacemassbalance
inaregionalclimatemodelofAntarctica.
Dissertation
zurErlangungdes Doktorgrades
¨inderWissenschaftsdisziplinPhysik der Atmosphare
eingereichtan der
Mathematisch-NaturwissenschaftlichenFakulta¨t
derUniversita¨t Potsdam
von
KseniaGlushak
¨Stiftung Alfred-Wegener-InstitutfurPolar- undMeeresforschung
ForschungsstellePotsdam,TelegrafenbergA43,
14473Potsdam
Potsdam,Dezember 20072
Idedicatethispieceofworktomybelovedfamily. MyparentsDinaandNicolayandgrand-
parents Galina, Boris, Zachar and Tomara who brought me up as a respectable, decent person
and always believed in me. My sister Elena, who taught me to dream big and never give up.
My”bigbrother”Michail,whosupportedand protected me.
Loveisall around.Contents
1 Introduction 5
2 ClimateofAntarctica 8
3 HIRHAMmodeldescription 14
3.1 Governingequations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2 Boundaryrelaxation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.3 Initialisationoftheprognosticvariables . . . . . . . . . . . . . . . . . . . . . 17
3.4 Vertical,horizontalandtimediscretisation . . . . . . . . . . . . . . . . . . . . 18
3.4.1 Verticaldiscretisation . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.2 Horizontaldiscretisation . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.3 Timediscretisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.4.4 ModelsetupforAntarctica . . . . . . . . . . . . . . . . . . . . . . . . 20
3.5 Parameterisations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4 Datasetsandcomparisonperiods 28
4.1 ERA40andNCEP-NCAR re-analyses datasets . . . . . . . . . . . . . . . . . 28
4.2 Radiosondedata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 AVHRRdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.4 Totalwatervapourdata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5 Modelvalidation 32
5.1 Meansealevelpressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2 Geopotentialheight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.3 Airtemperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5.3.1 Surface temperaturebasedon thesatellitemeasurements . . . . . . . . 49
5.3.2 Verticaltemperaturestructure . . . . . . . . . . . . . . . . . . . . . . 50
5.3.3 Surface temperatureinversion . . . . . . . . . . . . . . . . . . . . . . 51
5.4 Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.5 Cloudcover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.6 Surface radiationbudget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.7 SensitivitystudieswiththeHIRHAM model . . . . . . . . . . . . . . . . . . . 69
5.7.1 Planetaryboundarylayer . . . . . . . . . . . . . . . . . . . . . . . . . 69
34 CONTENTS
5.7.2 Cloudcover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.7.3 Lateral boundaryconditions . . . . . . . . . . . . . . . . . . . . . . . 76
6 ThesurfacemassbalanceoverAntarctica 82
6.1 Total watervapour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.2 Net surface massbalance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.3 Blueice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7 DecadaltimescaleprocessesoverAntarctica 94
7.1 Temperaturetrend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.2 Pressure trend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
7.3 Net surface massbalancetrend . . . . . . . . . . . . . . . . . . . . . . . . . . 102
8 InfluenceofAntarcticOscillation(AAO)ontheregionalAntarcticclimate 106
8.1 Mean sealevelpressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
8.2 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
8.3 Geopotentialheight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
8.4 Precipitationandnet massbalance . . . . . . . . . . . . . . . . . . . . . . . . 120
9 Conclusions 124
A Standarddeviation 128
B Modeldescription 135
C ListofAbbreviations 136
Bibliography 137
Listoffigures 145
Listoftables 155
Acknowledgements 157Chapter1
Introduction
UnderstandingtheEarth’sclimatesystem,particularlyclimatevariabilitypresentsoneofthe
mostdifficultandurgentchallengesinscience. TheAntarcticistheprincipalregionofradiative
energydeficitandatmosphericcoolingandbecauseofthis,itsroleintheglobalclimatesystem
iscrucial. Throughanetheatingofthetropicsandacoolingofthepolarregions,thezonalmean
radiative heating of the atmosphere generates a meridional energy gradient. It subsequently
influences global circulation; this occurs through the meridional energy gradient between the
poleandthetropicalregionandontimescalesrangingfromthesynoptictoseasonalanddecadal
scales.
The ice sheet in Antarctica is an important element of the global water cycle. By storing
large volumes of fresh water as ice or ice lakes, and by sometimes also releasing that water, it
canaffect thesealevel,globalocean circulation,and hencetheEarth’sclimate.
Thegoalofthisdissertationistoimproveourunderstandingofthekeyprocessesanddecadal
scale changes that occur in Antarctica and that also control the regional climate. Potentially,
suchprocessesandchangeshaveglobalimplicationsand consequences.
BeforeitispossibletoaccuratelyassesstheroleoftheAntarcticintheglobalclimatesystem,
it is necessary to understand the key processes of the regional and meso-scale meteorology
and dynamics. Projections of the state of global change must accurately account for Antarctic
atmosphericprocesseswhoseeffectsaretransmittedtotherestoftheplanetviaatmosphericand
oceanic circulationpatternsand currents. In addition,the processes by which tropical latitudes
impacttheAntarcticarenotfullyunderstood.
The main features of the Antarctic climate are as follows: low surface temperature, strong
surfaceinversion,persistentstronglow-levelwind(alsoknownaskatabaticwind)andlowpre-
cipitation rate. The Antartic’s main processes make an investigation of this region’s climate a
real challenge. Antarctic’sremotelocation,itsdistancefromothercontinents,itshightopogra-
phyand thesparseobservationaldataavailableforitdonot makethetaskat hand anyeasier.
To model atmospheric and surface processes at the regional scale requires a sufficient hori-
zontal and vertical resolution. This is, especially the case in mountain regions that are situated
56 CHAPTER 1. INTRODUCTION
along steep topographic gradients and is also the case in areas that have complicated land-sea
contrastsorareaswherethereisapresenceofsea-ice;allofwhicharecharacteristicsofAntarc-
tica. Present-daycoarseresolutionglobalcirculationmodelsandthere-analysisproductspoorly
represent the hydrological cycle on a regional scale. Regional climate models can realistically
describetheregionaldistributionofprecipitationand accumulationpatterns.
◦Instrumentalrecordsshowanincreaseofapproximately0.6 Cintheaveragedglobalsurface
air temperature in the 20th century(the average of near surface air temperature over land and
sea surface temperature). The IPCC (Intergovernmental Panel on Climate Change) projects a
◦1.4 to 5.8 C increase in the global average surface temperature in the 21st century. Despite
this,recent studies(Comiso,2000; Doran et al., 2002; Chapman and Walsh,2005) reveal a net
surfacecoolingovertheAntarcticcontinent. Also,becausetheAntarcticicesheetcontains70%
of the fresh water, whichcan be released due to increases in temperature, another pressing and
globalquestionistheriseofsealevels. Therefore,itisworthinvestigatingthenetmassbalance
accumulationtrend. Davis et al. (2005) used satellite radar altimetry measurements from 1992
to2003todeterminethat,onaverage,theelevationofabout8.5millionsquarekilometersofthe
Antarcticinteriorhas been increasing. The increasing elevationwas then linked to increases in
snowfall,whichwastranslatedintoa mass gainof 45±7 billiontonsper year, tyingup enough
moisturetolowersealevelby0.12±0.02millimetersperyear.
Natural climate variability is also likely to affect future Antarctic climate evolution. This
is because, recently observed climate changes over southern latitudes can be at least partially
attributed to changes in the atmospheric c